Or that most of the largest opportunities have been filled and newer companies are aiming at much smaller niches, or to be alternatives to well-established competitors.
Also, in 2005 there wasn't that much of an acquisition ecosystem. I feel like fewer founders back then actually thought about getting acquired and instead shot for building big companies.
You had to go big or your thing would fail, whereas nowadays you can fill a tiny niche and get rich by being acquired by the incumbent you're a complement to.
The era of "any promising startup gets swallowed by big tech" seems over with antitrust, but M&A is still happening.
