Why not buy an iPhone 15 Pro Max instead of a camera system costing more than 1500?

Why not? Because phones are effing horrible things to try and take photos with. An uncomfortable, cramped, frustrating & unenjoyable experience for me. Sure, you could add some sort of grip to fix some of that, perhaps an EVF, maybe some manual control points, but then what would you have? Yeah, a camera.
I have zero intention or desire to carry a camera around in my pocket, or my phone a lot of the time for that matter, so the size reduction over my m4/3 cameras holds no attraction to me either. I have a small shoulder bag that my camera, wallet, another small lens or two and a small bottle of water reside in, that's all not going to fit in my pocket anyway, so I may as well get comfortable, & use something that's actually a pleasure to use.
Oh, size comparison. One of my G100's that takes most of the photos I post here. With a 24-64mm equivalent lens.

With my latest acquisition, the little 14-42 power zoom.

In contrast, I will make extraordinary efforts to avoid carrying a bag. This despite my having quite a collection to choose from when compelled. (With opinions to share on every one of them.) The phone rides comfortably in my left front pocket. Wallet, stripped to the bare essentials, and car fob in the right. (I wish the function could be moved to the phone.) If I carry the X100V it’s often in the belt holster I purpose made, along with a spare battery (and/or WCL) in a shirt or jacket pocket. I have a small sling to carry the entire kit when I so desire, but I’m happiest when I’m unburdened by a bag that needs tending.

I made a holster for the phone too. I sometimes use that if I’m doing a phone-photowalk.

Options.

I was in a ten days road trip from Banff to Jasper in Alberta Canada. Let me say this, it was the largest amount of dedicated cameras, mostly mirrorless, that I have ever seen in the wild. It must have been easily hundreds of mirrorless all along the tourist spots on Icefield Parkway Road. I saw a bunches of long white Canon lenses, some Nikon Z, several dozens of Sony, and surprisingly dozen of OMD cameras with long lenses too. Most people who carries mirrorless cameras speaks French, but most Asian and US tourists used phone but not the the usual scene of hand up skyscraper imitation. There was some type of photo club pulled over where I stood the disembarked two dozens of shooters of all makes, happily clicking away.
I am saying dedicated cameras are still very much alive and well. Phones have its place, but I rarely use mine.

I compared my little iPhone SE (3rd generation)
With four different-generation cameras in 10-year increments: 2022, 2012, 2002, 1992

iPhone SE (2022) / Fujifilm X-T5 (2022)
www.flickr.com/photos/maoby/albums/72177720304286103
2022

Fujifilm X-Pro1 (2012) / iPhone SE (2022)
www.flickr.com/photos/maoby/albums/72177720306851990
2012

Canon EOS-1Ds (2002) / iPhone SE (2022)
www.flickr.com/photos/maoby/albums/72177720303321423
2002

Kodak DCS 200 (1992) / iPhone SE (2022)
www.flickr.com/photos/maoby/albums/72177720299521535
1992

An amusing comparison of the evolution of digital technology over the last thirty years.

*Personally I have a lot of difficulty using my iPhone as a camera.
The handling is too unpleasant, but I am able to be in awe of the technological feats achieved over the last 15 years.
And to understand people who prefer to use their smartphones, for many reasons.

I like the cut of your jib!

Complete waste of time- Just don't buy into the cellphone bollocks!

Precisely, along with many other annoying things.....

There's also the small matter of price. Here in Aus, the iPhone 15 Pro will set you back $2200.
One of my G100's was $475 brand new, the other $510. The zoom lenses were around $200. My Oppo phone was $400. And does everything and more I require.
So there's that.

Yes, for that I could almost buy a brand new G9 and two lenses

If you are happy with this quality and think that they are as good as you could take with a camera then use the phone. Looking at the images, the sunset bride shot is terrible, the foreground leaves image where the article goes on about how much better the detail is with the more expensive phone fails to point out that there is almost no detail in one and marginally less in the other. Sunset shots, fried egg in the sky in one and image 18 of 34, do you really think that the sky looks realistic? The images are almost all snapshots and when taken in good light they look fine, night mode looks good for a night time shot. I seem to remember previous claims about phones producing images as good as a camera and if that was the case then this new wonder phone must produce images that are better than the camera, is anyone claiming that? Stop improving phone cameras they are already as good as a camera and can produce wonderful prints up to 24" wide, do you really want that? Phone Good instant snaps, better instant snaps than previous phones, good images in good light and some people will think that you are brilliant because they look better than the previous generation phone images. Camera lots to learn, needs processing to bring out the best, doesn't give instant images to post and forget and the last point is probably the most important. Ken

Focal length range is the big one for me. I use a huge range of focal lengths, from full-frame fisheye through to about 4,500mm equivalent, that a phone just doesn't come close. Phones are also ergonomically horrible and a massive displeasure to use.

It really does show how different humans are. I, personally, find that smartphone cameras are more pleasurable to use. I, personally, find them light, easy to hold, and easy to use the camera in manual mode. I also understand that you simply don’t like them.

I will freely admit that as a person who had used a viewfinder/traditional bodied camera for 45-years a smartphone form-factor was jarring — at first. It took a while — several months — to really get a “feel” for a smartphone camera. For the work I do I have come to appreciate much of what a smartphone camera has to offer me and it has become my camera of choice (with the exception of things like Birding where long glass is needed).

Typo...let me correct that for you - It really does show how stupid humans are!

Yes, humans are stupid. You’re human, Right?

I notice how extra human you seem to be...nést pas? You must be special needs for being a phonetard promotor/user!