I think alot of objectification is motivated by sexism.
However I would argue that objectification plays a large part in Human mating biology, and therefore is predominantly not motivated by sexism.
Appreciation for the physical appearence is the first stage of attraction for men, in broad strokes, which is a biological thing, not social conditioning. When we see a woman for the first time we look over their bodies and our minds make a snap-decision on her worth in a relationship, completely independently of what their personality may be like, because fertility doesn't give a shit about your ph.D
Men may appreciate their personality later, but the initial phase of attraction for most men is basically objectification. In fact, you could say that we objectfy women, sub-conciously, dozens of times every single day.
This type of objectification is the most common form of all, and I would argue that it isn't sexist. Therefore on average, objectification is not motivated by sexism. Men just have a predisposition to make initial judgements based off of appearance.
EDIT- And please don't mistake this as a form of deterministc argument. I'm not trying to justify any kind of behavior.