Interesting story in particular, but in general, performance and memory behave like any other resource that is plentiful: they get used up until things are slowish again. Like road space. Things get added on top of each other until the reduction in speed becomes visible.
Because these days, unlike in the 90's, it's no help waiting for the next Pentium processor to come out this usually results in a heavy optimisation cycle in the underlying engine. For example Firefox has advertised a speed-up several times in the last 10 years, each coming from a focused effort to rewrite or optimise the JS engine, the rendering engine, or something else. Then things accumulate again, until things are too slow.
Obviously the cycles aren't wasted as you can do things with a few lines of high-level script that would've taken months to implement in the "good old times". But this development inevitably creates bizarre flashbacks where, occasionally, you're doing something simple like typing text on today's monster machines and it takes a few seconds for the screen to catch up your typing.
When I started programming, things were roughly and more or less instant. Typing was instant. There was a very short code path from handling the interrupt to updating screen. The computers reacted more like physical apparatus. Terminals at shops, warehouses, hospitals, with text-based programs to update data were pretty much instant too. Good clerks could bang their keyboard through multiple subscreens of their program in seconds, and you were checked in, goods reserved, or patient data updated. Later, when multitasking hit the mainstream, flipping between programs was instant. (Not on Windows, though.) Things like I/O took its time, of course, but at one point there was a peak moment where a software machine had nearly as low latencies as a physical machine.
From those times things have mostly gone downhill. Yes, we have immense processing power and near endless fast memory and disk storage. You can switch between browser tabs 300MB each pretty fast but there is a constant, nagging sense of slowness present all the time. Maybe sometimes switching that tab or bringing up another program takes longer, surprisingly, or there is something simple that just doesn't happen right away. The feeling of instant responsiveness is broken into shards: you can still see a reflection of it if you happen to look at the right angle but mostly its crumbles are pointing elsewhere.
Things like BeOS tried to reach back to that, with varying but acknowledgeable success. But real success in terms of popularity and market penetration seems to come from piling up stuff until things get too slow. So I doubt we never get back to the old world of instant response in spite of processing power keeps climbing up.