The point is that the lawsuit is your leverage for the negotiation. The acquirer doesn't want to see you lose the lawsuit any more than you want to lose it, because it would set a precedent that would make their own products infringing. And since they're bigger than you, they have more to lose, and hence more of an incentive to win.

I've long suspected that Google bought YouTube for the lawsuit. If Viacom had won, it would set a legal precedent that would basically make Google's business model illegal. And Viacom would likely have won, suing a tiny 14-person startup. So Google's only option was to buy the lawsuit (and the company along with it), so they could use their own legal defense team to win in court.

I think you're out on a limb a bit with this one. For most people and companies a lawsuit would most likely be considered a liability. Granted that there are exceptions like the YouTube example you propose, but you can't assume the same for every little startup that gets sued.