Thor is loyal to a fault. Taking advantage of him was much easier than taking advantage of everyone else.

[ Especially since his care for actually being a good person, this time around, was pretty rock solid. ]

Aye, 'this time'. Thor had to die when the Serpent attacked, did he not? Through a series of amusing and quite fortunate events, Thor came back.

Then I drowned him in a pit of lava.

[ No big deal. ]