It's probably because oddsmakers add context to the reasoning behind their lines.
Davey Grant has gone 3-2 in the 5 years and 4 months (less than 1 fight per year average) since their first fight and it's been against lower tiered prospects. Losing to such "names" as Damian Stasiak and Manny Bermudez.
Meanwhile, Chito Vera has gone 9-4 since then (almost 3 fights per year), gradually improving his overall skills and rankings, against mostly tougher competition along the way. Out of his 4 losses, 1 was against Aldo in a fight Chito probably won and another was against Lineker when he was a top dog, by decision.
I like Davey Grant and he deserves this fight, but Vera is taking a step down to reclaim an old loss and the betting lines make sense for that.