From the acquirer's side, I'd guess competitive reasons. The amount they were willing to pay sends a signal to their competition about how important that particular product is to them (and if they paid a lot, that message is often very loud and clear).

From the seller's side there's the issue of respect for the acquirer's preferences as well as the fact that broadcasting your payday is kinda like broadcasting your salary: It can create some awkward situations. Especially if you're trying to keep some non-owner employees around.