Using the vBulletin's reputation system was more time consuming and people did not use it so much (they had to add a comment too). Now you just click the Like button and that's it.
True! And it had limits (how many you could give per 24 hours and a wait time until you could give again to the same person). Now it's much better and all that's needed is a dislike link next to it. Even if dislikes were to be shown privately (I guess public ones would upset a lot of people).
I think the philosophy from the like is "How to make other people happy with you". You will get like when you make people happy. Sometime you have to thinking, that it's not about money. But, it's about carrying.