Most of the applications I work with today do a lot, that's true, but their UI latency is often worse than it was on my 7.16Mz M68000 Amiga 500, and other things as well are just slow.
I've mentioned here several times in the past that on my laptop I can "boot" Linux-hosted AROS (so the problem is not the Linux kernel, nor X) with a custom startup script to boot it straight into a full featured, scriptable text editor in less time than it takes to start Emacs.
I'm sure it's possible to tune my Emacs setup (for example, I found out by a fluke, that the default Emacs setup on debian will wait for a DNS request to complete or time out before it starts - break your DNS setup and Emacs will hang for ages) or pick another editor (many of the other ones I've tried are either just as slow or feature-limited compared to the Amiga editor in question - FrexxEd, co-written by the same guy that started curl), but the point is that we've come to accept the kind of slow startup and UI latency that was unacceptable back then.
E.g. people spent weeks tuning and trimming AmigaOS commands to make them the smallest possible so we could make as many of them as possible RAM resident to avoid the tiny fractions of a second it'd take the load-time linker to load them.
I'm happy we don't need to think that much about the RAM any more. But we do need to think about the latency.
There's the attitude that we should just throw servers at this instead of developer time. That's fine when you can compensate by e.g. throwing more RAM in and/or a program is run relatively rarely or where paying for a beefier server in some data centre can achieve the same performance. But it's not true when latency grows into user noticeable levels because you can't get high enough single-core performance, and that program is run a lot.
On the other hand, I've been frustrated with the slowness of computers for a long time. CPU speed, RAM, disk, everything has gotten way better. But I'm still just about as irritated, and I suspect that things are just about as sluggish.
Again, I think it's an economic equilibrium. Things are fast enough that most people buy them; those of us who want things faster aren't numerous to outvote those who want fancier features or cooler UI bling instead.
I hope this changes, but I'm not holding my breath.
Extra weight will always matter for people who want to deliver first-rate user experiences.
But when I think about software as a business rather than an art, I have to concede that it's a very rare circumstance where RAM efficiency matters as much as I'd like. Note the way the cost of memory has declined:
http://www.jcmit.com/mem2015.htm
Watches now have 100,000 times the RAM that I started with. Costs are dropping by 1-2 orders of magnitude per decade. Something that is absurdly wasteful now could well be economically reasonable very soon.