The UFC saw the writing on the wall and got rid of him the moment they could. He was already in his late 30s attempting a new combat sport where he was largely untested in any meaningful way. It didn't even require him fighting ranked opposition -- or indeed, actual grapplers -- before he was getting tossed around and mauled.
I mean on paper Acosta and Lane were both softball lay-ups at the time. Lane is one of the chinniest Heavyweights I've ever seen and relies on his athleticism and length to win striking exchanges -- something he wouldn't be able to safely do against Robelis. In his fight prior to Robelis he tried becoming a grappler to beat a pure kickboxer, thus leading to him rapidly gassing out and getting murdered in Round 2. Acosta has aged better than I frankly ever expected, but he was still more or less viewed as a pure volume boxer with little to no grappling.
Robelis was never going to amount to anything and seemed unable or unwilling to shore up what was a massive hole in his game. And yeah I wouldn't be surprised if he got brought on at a slightly higher rate than the standard 12/12, but who knows?