Because he is a great and wise Jedi master?
Regardless, what I’m trying to say is that I don’t understand what your larger point is.
Right. So…Yoda would have been in the movies even if Ben hadn’t died in the first one?
Could have, certainly, would have, I don’t know. Again, I’m not even sure what the point of this hypothetical is.
The point is that if Lucas only* introduced Yoda because he killed Ben off, and otherwise wouldn’t have introduced a strong and wise Jedi Master character into the trilogy, then it shows that Lucas’ penchant for making things up as he goes along was something that goes back almost to the beginning of Star Wars. It’s not something that he just started doing with Return of the Jedi. The same goes with Ben’s character. The character of Ben Kenobi was created to take the place of the father character who had been killed off in the story (as of the third draft), whereas prior to that he was to have been still alive in the story (in these earlier versions, Jedi knights trained their own children). So, as Yoda was a sort of ‘proxy’ for Ben, Ben himself was a ‘proxy’ for Luke’s father.
My overall point is that the “shrinking-universe” phenomenon is part of Star Wars’ “dna”, if you will
*Lucas himself even said that prior to killing off Ben, when thinking of potential sequels, he wanted Ben to train Luke in the other two films and then maybe have him die in the third.