Twitter's native app is heavier than their web app because Twitter has historically filled the native app with junk (like a fullscreen video just for the login screen, "moments", "highlights", hijacking browser URLs, a bunch of ads and ad tracking, etc). Facebook does the same, to an almost silly degree - https://news.ycombinator.com/item?id=8162342
The Twitter client could easily be ~3MB on Android, for instance, if they just stripped the garbage out. And similarly, if you take a web app, and embed all that same junk into it, it will suddenly be a heavy download too.
According to this, Facebook was 32 MBs 4 years ago. It's similar with Twitter.
It's their fault that they keep adding stuff to track you. And Facebook contains just about every library that has ever existed now.
I remember Twitter.app had code to get the currently installed apps, to "better target ads." It's user hostile and we are paying with the multi gigabytes of data.