Bosses dont want you to give you good references?

I have a question, I heard people said that if a worker does good his job ask for more
Overtime, or ask a reference to the boss but in most cases I think they dont want you to give you good references even if you work well. Because they think that you want to leave his job. Tellme if iam wrong what do you think about that.

I think you are right. I had that happen before.