This is something that I see espoused by "web traditionalists" for lack of a better term. Sure, there are a lot of web developers who are not optimising for performance but I think the difference is that it has simply shifted to the frontend where it's more noticeable. The kinds of people who care about performance in the backend are exactly like the kinds of people who care about performance in the frontend. There's…
Actually the funny thing with HTML is that the simplest things are fast. If you just write a old school HTML web page without a bazillion frame works and not going too heavy on graphics things are usually fast.
And doing that is literally so much simpler and easier than learning all the super complicated frameworks of the day.
So it's a progression from initially fast for simple, to slower and slower as people learn the complicated (and slow) frameworks, and then eventually maybe fast again if you have an expert who can make all this mess fast again.
Most people never reach that expert stage of course, but sadly still leave the "easy and fast" stage.