It's often a "let's recoup our losses" move for the investors.
People want to be successful. One of the clearest ways that success is measured in the startup space is by a larger company buying you out.
Of course they're excited.
Getting acquired doesn't have to feel so bad for a startup. The optimist can see it as a way to continue working on their project without worrying about profitability or investors, and the pessimist still got paid.
I mean, you could very well see this kind of company merge with people doing an advanced IDE, or even corporate frameworks.
Maybe they usually prefer to create commercial partnerships rather than merge shares.
Merging with a similar sized company means relinquishing control for no immediate return.
Small and medium sized companies merge all the time (but its rarely big news, because small companies), but "promising" ones in the Silicon Valley swing-for-the-fences startup sense probably don't as much, probably because that kind of merger doesn't provide the kind of exit startup investors are looking for or increase the perceived likely size of the eventual exit enough to warrant the dilution.