Even Yoora Jung was job hunting after getting her degree (she also plans to go to medical school I believe), people in the comments were all "she's got 1M subs what's she looking for a job for?Yeah, that’s not going to happen with most of the UK StudyTubers, I’m afraid …
You can do very well with Youtube but it does help to have other skills than studying when it comes down to it. You're only in school and university so many years, it helps to build experience and skills outside of that (even if it isn't necessarily full time).
The Studytube community is not what it used to be either, it's become very saturated and younger people have a greater tendency to want to watch newer studytubers just starting uni they can compare to over ones that have been making the same types of videos for 5 years like Ruby has.