The problem is that in current app stores, there are no easy way to find apps that match your hardware requirements. If I want a fitness app that I didn't think of installing when I got the device 5 years ago, I can't easily look for one designed for 5 year old phones on the App Store. Or an app that developers forgot to update/bloat for the last 5 years.

Also, sometimes you don't have the choice. The app for the public transportation in my city is quite heavy but there is no alternatives except queuing for a paper tickets. And I would bet that most users would be absolutely fine with a leaner/faster app.

So sure, you have to keep up with the time but to me, it feels more and more like a wasteful flight forward anyway.