But how would you express nuances in certainty?
There are things I know, and there are things I believe are probable. Are you saying I should not talk about the latter or leave out the information of certainty for you?
Agreed. However you can also see that Elon doesn't seem to be all too eloquent in his speech or comfortable (at the time anyway), which may account for it. In addition, you can tell that he hasn't necessarily planned out what he's saying here. When he uses "I think" it sounds like it's a thought that he has just then constructed -- as in what he's saying is intuitively correct -- however he seems to realize himself that what he's saying may not be universally true.
Say what you believe, like you believe it. We already know it's your opinion, you're the one saying it. Saying "I think" just makes you look weak and like you don't believe your own words.
It's mostly just annoying, not a sign of humility. A sign of humility is talking in absolutes and changing them when new data is available.