@Doomer It's all a balancing act of freedom vs security. Currently he's a slave, but he has a home, food, friends etc.. He's being trained, and probably educated. So far, nothing indicates he's being treated as anything less than a normal employee, since being bought. He has a somewhat secure life, despite not being 'free'.
Now say he broke free, and left. He now has no home, no food, no money, no allies. He will now be hunted as a runaway slave. The only thing he has is the skills and knowledge his 'owners' gave him. But since he's hunted, he can't live in society. He'll have to live in the wild, fighting for his life everyday. He now has freedom, but literally
no security.
It works like this in our world too. You give up small freedoms, having to follow laws. You gain security because the laws are enforced on everyone (well, in theory, anyways), protecting you from murder and the like. You can't have full freedom and still expect security. If you're free to ignore the law, your neighbour is free to kill you and take your stuff.
Now, I'm not saying slavery can be accepted, it's a horrid thing. I'm just saying from MCs point-of-view, this is the best option he has.
Edit: My spelling sucks, fixed.😉