There isn't necessarily rationality behind venture deals; its just a numbers game combined with the rising tide of the sector. These firms are not Berkshire. If the tide stops rising, some of the companies they invested in might actually be ok, but the venture boat sinks; the math of throwing millions at everyone hoping for one to 200x on exit does not work if the rising tide stops.

They'll say things like "we invest in people", which is true to some degree, being able to read people is roughly the only skill VCs actually need. You could probably put Sam Altman in any company on the planet and he'd grow the crap out of that company. But A16z would not give him ten billion to go grow Pepsi. This is the revealed preference intrinsic to venture; they'll say its about the people, but their choices are utterly predominated by the sector, because the sector is the predominate driver of the multiples.

"Not investing" is not an option for capital firms. Their limited partners gave them money and expect super-market returns. To those ends, there is no rationality to be found; there's just doing the best you can of a bad market. AI infrastructure investments have represented like half of all US GDP growth this year.