well, even the most feature-bloated IDE loads faster than GMail on my computer (before anyone asks, I'm on gigabit fiber)
It may be a controversial opinion, but I think part of the problem today is that young web developers look to people who work at high-profile places like Facebook and Google as role models and for examples of best practice. And yet, a lot of Google's and Facebook's own web properties are... less than exemplary... in terms of performance, usability, design, and other factors that are important in most situations, and have been getting steadily worse rather than better over time. I humbly submit that the reasons for the runaway success of these giants have really very little to do with the quality of their sites any more, and that up to a point they can get away with things because of their dominant positions and lock-in effects that simply wouldn't be acceptable for most of the rest of us.
Now a future programmer three years later tells the business manager that they can do this much better now for $x. It will improve nothing as far as the user in concerned. Maybe the page will load faster but the user may not even notice. Maybe they will save some money on hosting and bandwidth costs.
In most cases, the business person will most likely tell the programmer to keep working on to new feature z2021 project and leave the old code alone. This is until there is a security problem or the old code effects the z2021 project.
There was a study that has shown correlation between revenue drop and milliseconds that page takes to load. It’s not only hackers that respond to performance.
As for competition - due to network effects there are very few competitors to things like Facebook, Amazon and other big tech.
If these were federated services participating in communication built around some gigantic independent social graph - that would enable more competition in terms of UI performance, features, etc. Not going to happen anytime soon though.
(Spoiler alert: If your system is well-enough implemented to be correct, it is well on the way to being secure and performant too)
For user-facing applications performance only really matters in human time, and is pretty far down on the list of how people choose software over things like features, price, ease of use, etc.. Until performance becomes a big problem because the app/site becomes unusable it's basically no problem.
Hackers might not like it but we're such a weird market to sell to. Not necessarily that performance is a weird preference but that by in large hackers are perfectly fine with woefully inefficient feature-packed apps for their "primary" apps like their IDE but then want super lightweight skeleton-featured experiences for everything secondary.