I think the reason it's a thing is the same as the reason Hollywood exists and Las Vegas exists. Overabundance of inhumanely rich idiots that are bored and want to gamble. And they do because they falsly believe they have an edge in their bets due to their secret knowledge of the game and unique talent in picking the right horses. Most of them will lose most of their bets. But a handful of wins is more than enough to write about to draw in next batch of idiots or even the same idiots again if they still have money to lose.
Yes, I know. But in the US this is not considered a lot of money - they actually got considerably less money they could've gotten if these founders had a product in another market. And, making the money back in the US market is easy - this is really not a lot; just 5-10 senior engineer yearly wages...
The lower the interest rate, the sillier the investments.
The goal nowadays for these kind of tools is to get bought out by platforms such as Vercel/Fly/etc. or to become a platform of their own. Given that devs these days are afraid if not unable to deploy a React website on a VPS by themselves, it's become a self-sustaining lifecycle.
This tends to be a particularly US phenomenon. It's a house of cards waiting for the next shaky economic phase.
Every build tool was obscure at some point. A common monetization plan for these is cloud services (promising faster builds and such) with usage-based plans. A few enterprises may use these services over time; for one project I'm at they're considering e.g. Expo and its cloud / CI offerings, because spinning up and configuring your own Mac machines in the cloud is painful and expensive.
https://voidzero.dev/posts/announcing-voidzero-inc