They have a very concentrated form of koolaid over there. I've been surprised by the effect it's had on some of the most skeptical people I know.
Sure, there are many other possibly "better" ways to touch peoples' lives, but I'd much rather do something I love doing that also helps people than hate what I do. We can't be completely selfless.
Well, startups aren't the only types of companies that get bought. Acquisitions are part of the markets and across all types of companies, big or small, young or old.
The only difference is that the tech startup scene is so very loud and vocal about all this. In other markets, it's maybe a side notice in a rarely-read corporate newsletter. Nobody cares except for the individuals directly involved.
Ultimately, the bulk of these M&As happen not because a product is to be destroyed but in order to take it to another, subjectively "higher" level. It's the same here. Whether that happens, as always, remains to be seen, but both parties were willing to try.