Nice!
I think there are a few factors at play here in the phone hardware market:
-Like 10 years ago everything was new and excited with smartphones. Huge tech advancements from model year to model year aside, there was some really cool stuff going on. Screens making massive leaps in resolution and OLED technology, cool designs and finishes, slide out keyboards, flip out keyboards, 3d screens, 3d cameras, projectors built in, etc. Form factors and finishes were more varied, and OS skins were more and more unique as all the manufacturers were trying to figure out what worked. Over time the same basic design just took hold and completely dominated (not really a bad thing at all) and now almost all phones more or less look and function the exact same way. Same with Android OS skins (again, not a bad thing as Android is so much better these days). No one is buying the newest HTC phone because the new Sense is amazing. So upgrading your 3 year old phone now comes down to it's a bit faster maybe, the camera is slightly better, and the screen might be better. You used to get those kind of jumps month to month basically.
-Phones cost way more, inflation taken into account. I used to kind of want to buy a new phone every year or so (obviously didn't unless I broke it -which happened) and it was at least feasible, if not entirely responsible or a good use of money. But if you were a gadget guy you could at least justify it. The Nexus 5, even with inflation would be quite a bit under $500. Pixel 3 is twice that I think. Even the Pixel 3a is at least $100 more. On the main/high end it's far more pronounced as well. The Galaxy S10 is like twice the price that the S2/3/4 would have launched at, accounting for inflation. Shit yeah, it's a lot nicer but you're only buying one when you absolutely have to. I think the flip side of this is that the low end lines like the Moto G etc are now very cheap and way more functional than they used to be. But those aren't the lines that ever excited people.
-The marginal difference in upgrades is way smaller than it used to be. Designs and price aside, if you upgraded a 2009 phone to a 2011 phone you were probably blown away. Dual core CPUs running at least twice as fast, way way more RAM, GPU, etc. All that is so well advanced now that the steps don't feel at all exciting. They ARE faster, but unless you're looking to play Fortnite, etc you're probably never going to notice. Instead most people are probably just looking for more storage when they upgrade and the base model storage is so slow to increase because the higher storage upgrades are so profitable.
Along with the novelty of Smartphones being common for a decade plus its combined to make it a market where sales have definitely slowed. There are way less shitty phones flooding the market but it's also far far less exciting or enticing for consumers. If you look at Android news sites, reddit, or forums all the buzz is around "teardrops" and bezels - terribly boring.
