How is he supposed to "earn" it? Like I said, he had a 110 OPS+ last year in his first season. That makes him a little closer to an established MLB hitter than the other guys we're talking about. Plus he's had injury issues this year.
It's pretty hard to earn anything when you're not in the lineup.
I think Cora is a master at juggling all the lineup conundrums and giving everyone a fair shot.
If Yoshida doesn't start to produce, at some point he will get squeezed out. But that time isn't here yet.