Jays have some top 10 prospects playing SS that are expected to move off the position. Groshans, Orelvis, Martin, Hiraldo all have position questions and the general expectation is they will need to move off SS.
It would be an easier decision to give him starts at 3B if there was a true SS prospect on the near horizon. As long as he is deemed fixable as a SS, and I think he is, it makes sense to keep starting him there. He'll make a few more errors than a Semien, but that's probably an OK tradeoff in the circumstances.