It's hard to know if that's really true. I've been here years (not under this account) and can't say I noticed any obvious trend towards talking about the past more.

Still, speculating is irresistible so here's my 2c. It's because tech is relatively stagnant at the moment.

i. A lot of traditional "hacker" stuff is about how computers work/are designed, but innovation there has largely stopped. If you look at the newest operating systems (Android, iOS, ChromeOS, Fuschia), they're all extremely same-y. The web meanwhile is kind of more grown or discovered than designed. To the extent these platforms do things different from 90s era operating systems, they're trying to make things less hackable and powerful in order to increase robustness and simplicity. Three come from a single company (or four if you count the web), and reflect the mindset/culture of that company. So people who hanker for the hacker spirit look backwards to an era when how computers worked was still up for grabs and was at least some interesting competition of ideas.

ii. PL theory is likewise kinda stagnant. HN gets excited about Rust partly because it's the only new language for a while that has new ideas in it. Go, Swift, Kotlin etc - all nice langs but very much of a muchness and avoid new ideas (maybe Swift gets some credit for trying stuff with strings). Compare this to the days when C, Lisp, Objective-C, Haskell, Perl were duking it out. All very different paradigms and approaches. People who get absurdly passionate about PLs are kind of an anachronism these days but were once common because there used to be more at stake.

iii. Hardware: also stagnant outside of mobile. This is mostly the fault of Microsoft and Linux vendors IMHO. The mobile industry has shown that it's perfectly capable of doing cool stuff with hardware over the past 10 years, with folding screens being one of the latest gizmos we get to play with, but how much of that stuff made it to the professional workstation-class machines we actually use daily? Almost none! Even hiDPI screens are a trainwreck. The problem here is firmly in the software camp. Microsoft checked out mentally years ago, Linux is hostile to HW vendors doing new things because drivers are such a PITA to ship out of the box, and PC/hardware vendors can't do anything meaningful with Windows other than try to optimize cost. So the landscape consists of Apple porting HW upgrades from their mobile R&D, and that's about it.

iv. Web ideology has been fading with time and Google's dominance. HTML was never going to win any design awards but for years many hacker types were extremely loyal to it, perceiving it as an open system unowned by any particular company. Nowadays the loyalty is less, for various reasons. It's now OK to criticize it, it's not taboo anymore. People can look back on what it displaced and compare more rationally, hence the semi-common "Delphi was cool" type comments. This is a healthy pushback against the often irrational collective progressivism of the first decade of the 2000s, in which every "open" platform was cool, brilliant and the future, and everything privately owned was dangerous hot garbage. Sometimes I personally feel the pendulum has swung too far, like with the people who celebrate the inability to install non-Store apps on iOS, but there's no question that the pendulum has swung.