why does finn hate on him

The Force Awakens novelization gives Poe more depth as a character than the movie does. Mostly when Poe is intent on destroying everything in sight as he flees with Finn.

You get passages where both General Hux and Finn are wondering why the hell this guy is sticking around to blow up everything in sight instead of,you know, simply getting away at lightspeed like he should..

But as Poe tells Finn   “Kylo Ren called me the best pilot in the resistance. And I’d hate to disappoint him.”

Kylo used his superior skills to screw up Poe and his cause. Poe is now using his superior skills to screw up Kylo and his cause.