If they're hoping for an OT in the draft to play day one, the possibilities appear to be Banks, Conerly, Simmons, and Ersery. They might need to trade ahead of Minnesota for some of these guys, who also needs OL help in the draft. Trading up in this draft should be relatively cheap compared to past drafts. I do wonder if there appearing to be potential OT(s) either at #25 or in a short trade up from #25 available was a factor here
If the plan is to sign or trade for a stop gap veteran at tackle, or to play Tytus and Fisher there, they could sign another second round toolsy developmental project like Cam Williams or Charles Grant
I think it's clear that they didn't want to pay Tunsil his next contract. His current contract is actually probably a good value the next two years, but he's going to want a top of the market extension. They could have waited and traded him after next season and had a LT in place for another year, or they could have played him the next two seasons and gotten the comp pick down the road while potentially dealing with him being upset about not getting extended, but I guess they wanted to go ahead and get the draft assets while ripping off the Band-Aid now