He isn't well liked. The dems ran a laughably flawed candidate against him. It's more that Kasich's flaws are well-known and there's no point in electing anyone with those flaws plus some.
OH voters aren't stupid. I'd guess any support he's gaining is folks seeing an advantage in having their guy in DC.
it was reported just this week he had 83% favorability as governor
Kasich badly damaged himself with NAFTA and TPP and rubbed feces in the wound by backing the disruptors. I think any support he gets now will be from the "But he's OUR bastard." contingent.