YC is likely in the same situation as a famous Hollywood studio: you can buy the buildings and the logo, but once the people leave, the value is gone. So there is nothing worth acquiring.
To wit, this is a lot of the reason the storied SF law firm Heller Ehrman collapsed a few years ago: a large group I believe simultaneously left the firm, and the firm had losses, and there was no capital base left to draw on to get over bad times (for the record, a lot of professional services firms like investment banks used to be organized this way, and in bad years, the partners would be responsible for recapitalizing the firm. This is one of the reasons you so frequently saw IBs and other similar firms so anxious to sell themselves in the 90s, and it was, in fact, the primary driver behind the notoriously secretive Goldman Sachs going public: they had people rejecting partnership because losses made it unattractive, and their capital base was too unstable to compete in the global big leagues when it was just partners).
That said, Heller was cobbled together through a series of acquisitions, most notably for the HN audience, the famed Venture Law Group. And it's not like this was all terrible, the firm lasted for well over 100 years.
Similarly, people have acquired real estate brokerage firms, where you'd think there'd be even _less_ of value to acquire, but they do it profitably. I think Cendant paid like $50m for Corcoran Group. Organizing people and assembling clients is difficult: if you can buy an organized group of people with an active customer list/market position...there is some value there, it's just not going to be at sales/earnings multiples we are used to seeing with companies that own technologies.