Since when is UX the cause of a need for third-party plugins?

LaTeX is an incredibly mature piece of software, since it exists for some 50 years and is (and was) incredibly popular. Of course newer players won't have as much ready-made plugins, let alone first-party packages for most stuff.

Latex surely had the exact same issue when it wasn't as mature as it is today, but in time people wrote plugins and in more time they were included as defaults.

Comparing them quality-wise on equal footing and proclaiming Latex better than the younger, less popular alternative with less developed community code is disingenuous at best.

And UI/UX has absolutely nothing to do with styling: both are features, and one product happens to have one while the other happens to have the other. They're not mutually exclusive in theory.

However, I will give in that usually resource limits mean only one gets included. But that's corellation and not causation: good UX does not cause bad feature parity. The core cause is both requiring resources and one is usually made the top priority.