The "tech guys", as you call them, are dogfooding the app and feeling the pain every day. Matthew — the CEO — is the biggest poweruser of them all and feels all the pain points, with his account being the worst-case edge case.
It's just that most of the money comes from consulting, and consulting customers care about new features, not performance or UX.
Which is btw not just a problem for Element — the other companies working on Matrix have the same issues, for the same reasons.
Discord can afford this level of UI polish because they're spending an order of magnitude more on dev salaries than the entire revenue of all companies working on matrix combined.