1. You don't call up those guys because they still have room to grow before they get here. Both of them are still teenagers. Yorke is a poor defender (he'd fit right in on the 2021 squad). Mayer hasn't ever played a season this long before. Plus, nobody is calling for A players to be called up. Once you get to AA, the chance is much more likely.
2. You aren't going to waste a call up on guys like Yorke and Mayer for contractual reasons (i.e. Super Two status). You won't mess around with their service time.
3. If the Sox really thought Yorke could play everyday at the MLB level going forward, they'd call him up. If he failed after being called up, I don't think it would affect his career going forward because he's just 19 and still has a lot more to learn.
In a vacuum, call them up. It wouldn't hurt their status going forward. Was Pedroia called up too early? Did that affect him long term? Was he mentally broken after 2006?