For most, it's hatred emerging from deep-seated bitterness due to Everton's being outside the elite clubs and competitions that the best footballers want to play for. When Lukaku said in the press that he wanted to play CL football one day, those with that inferiority complex translated it to: I think I'm bigger than Everton and I want to leave. Not true. He'd have stayed if we'd qualified. He was here for four years.
This season (and those before it, really) has proved that those who argued he was good enough to play for a top 4 club and his team mates weren't good enough 100% correct and those that argued the opposite completely wrong.