House elf loyalty to there master is not some thing I think happened over night. In the beginning it may have been what you could call slavery but after many generations thats the only life they know and to take them away from that is like taking them away from there home. If something wrong like slavery goes on long enough the victims may no longer feel like victims cause they feel that is there place in society cause thats the only place they know. Yes there are some revelutionaries in the house elf case Dobby but they are few and far in between cause the house elfs feel there only place in the world is to serve their master.