The stated goal is usually around saving money, although there are certainly other benefits.
Newton's Third Law states that for every action in nature, there is an equal opposing reaction, and consolidation is no exception.
I think IT vendors tend to push consolidation without a full appreciation for the very valid opposing forces. And I think IT organizations sometimes lack the will to overcome these resisting forces in pursuit of a better outcome.
Case in point: now that I'm at Oracle, I see these amazing cost-saving proposals around database consolidation. We're talking eye-popping big savings numbers, buttressed with a rock-solid justification. But I don't see nearly enough leaders acting on these opportunities.
Nobody's right, nobody's wrong -- but it shouldn't be that way.