He does not see you serve his agenda,

 

so he has little reason to praise you publicly.

Every boss has an agenda, if he is a good one. You don't either know or you know but don't care about advancing his agenda.

By separating you from the rest, he contains you, so that at least you are not an obstacle to his agenda.

You have a need to be praised publicly. Whenever you have needs, you appear weaker.

 Validate yourself.