Who said infinite? Startup founders that got investments have designed the exit points based on market conditions, and nobody would trust "infinite". It's just like stock investments (unless you "invest" based on feelings, of course) - you calculate the risk, the potential, and then you decide. Nobody reasonable puts "infinite growth" into their Excel sheets.
And yes, growing until that exit point is a lot of work - so it makes total sense people want an exit at some point.
No, that's not true. There are plenty of stable market capitalization, dividend-generating public companies. Their cap-to-EBITDA ratio is much smaller, but that doesn't change the fact.
Of course everybody expects the company to take advantage of opportunities - but it has to make economical sense. Nobody wants their company to try to grow so hard the whole company crashes.
And yes, growing until that exit point is a lot of work - so it makes total sense people want an exit at some point.