Software today is much more capable than it was 12 years ago.
Depends on the area. For most of the corporate world, nothing changed. Databases mostly work the same since the 80s, the only new thing since then are data warehouses and nosql variants, due to the sheer volume of data available nowadays. Office applications (Word, Excel and similars) are pretty much the exact same thing as 25 years ago. CAD and 3D modelling tools haven't changed much in the meantime, but hardware got much beefier, making part of the process faster.
So why shouldn’t the phone have similar memory requirements to a PC?
For the same reason you didn't need 8gb of RAM just to open fucking Chrome back in 2010. Changing tabs was as instant back then on a shit computer as changing apps is nowadays on any phone, with significantly less resources needed for that. Loads of apps are little more than glorified "single page browsers", they just load a special version of the site with a couple extra bells and whistles. You can very easily run Spotify, Youtube, TikTok, Discord, Gmail, Xitter and more on a single browser and change tabs instantly with a single click. The mobile browser experience with them is bad because why make it good when "the app is better"?
let me also remind you of the fact that the mobile gaming market is the largest of them all by far.
And most games aim at the lowest common denominator (both regarding phone specs and "type of game") because they want to reach the widest audience possible. A lot of people use Unity to make simple 2D games, yet that thing is bloated as all hell. Does it facilitate development? Absolutely. That doesn't excuse it for being a mess.
As a side note, did you know that the PS2 had 32MB of RAM and its main CPU was a custom RISC running at 300MHz? You know, the console that let people play God of War 1 and 2, GTA San Andreas. "Oh, but its sole purpose was for gaming and it had a specific graphics core" - true, but once your application is front and center in a phone, it can hog 90% of the CPU and eat any free RAM, which, if your phone has 2GB total, and ~1.5GB is used by other apps and the system, you still have some 400MB to play with. The OS can get in the way and does add overhead, which ends up mostly being extra CPU time.
And honestly, I don’t remember Android phones from over a decade ago ever actually feeling fast. They might have been all right for a while but, in my experience, old phones would usually turn into a slog quickly.
A Galaxy S2, back on release, was really fast compared to its peers. Once its specs became mid-low end, it started to feel significantly slower, that's true. Could've been the bloat catching up.