There are a few reasons why he's unsigned. For one he will likely become the highest or 2nd highest-paid tackle in football getting around a 22M a year average.
Secondly, per report NFL teams view him as a RT, not as a LT, and would rather pay him like a RT. I'm not sure why tho? It's true Orlando was maybe the best RT in the league with the Ravens but at LT he was still top 10 and is still a top 3 rush blocking tackle regardless of side.
I think it's important he goes to a rush heavy offense and a team that needs a tackle regardless of side.