Along with Jackson, Cory Gearrin also came to the Rangers in a clearly money-motivated move. Gearrin was excellent in 2017, but he's gone backwards this year. His strikeout and walk rates are actually better, but he's given up a lot of home runs this year. The obvious thing is that he's not getting enough groundballs, only 34% this year VS a 50% career rate. That may be all he needs to regain past form.
It's not a bad move for either team, as the Giants have two guys that can immediately take those roster spots and the Rangers get some bounceback candidates, one of which they're probably going to flip immediately. They also got a minor leaguer in the deal, too.