Liquidation preferences can dramatically change the math on how big an acquisition needs to be to be profitable for the founders.

Say you've got 3 founders who each want to make at least $2M for a startup they've been toiling away at for 5 years which has built something kinda-sorta useful but not a huge hit (that's roughly equalling what they would've made at Google/Facebook). If they took a $5M Series A at $15M post with 1x participating preferred, they need to sell for ~$17M to hit their target (the VC gets their $5M back, then $4M of the remaining $12M for their for their 33%, then 20% goes to the employees from the option pool, then the founders split the remaining $6M). If they took no funding, they need to sell for $6M. If they took just angel/seed funding for 25% of the company, $8M.

It's generally a lot easier to get acquihired for $1-2M/head than for $5M/head.

I'm looking at https://yclist.com/ (no idea how updated or accurate it is) and seeing a lot of companies are have been around for years and not dead or acquired that I've never heard of. I'm mostly referring to cos that have raised another seed or series A for a few mil and then just sort of lingered. I do not know of every 100 cos how many successfully raise another seed or series A beyond what YC provides (I would assume many do)