Most of the stocks in an IPO are purchased by investment firms or large corporations - so it’s extremely uncommon to have no willing buyers.

The IPO price usually also allows for a pretty decent discount on the projected valuation. So, those big investors are looking to get in early and get as cheap as they can. So for something like this, there will be buyers.

That said, entertaining the hypothetical where no one buys: the IPO is likely canceled, in the most hilarious embarrassment in a good while on the market. If just a fraction of the expected shares were sold, they may be subject to a mandatory refund. Then the company can regroup and try again later, or just take the embarrassment and go.

S&P500 lifetime inflation-adjusted return is 7-8%. meaning, if one put away 150K in the S&P500 at age 20 and worked for 40 years, putting away nothing else but gaining that inflation-adjusted 7-8 (conservatively call it 7), and then pulled out a measly 4%, allowing the remaining growth to account for inflation, they’d be pulling an inflation-adjusted income of >80K, ignoring any other income.

I’m not saying one shouldn’t put anything else away or strictly count on matching historical S&P return, but yes, putting away 150K at 20 could absolutely mean you don’t need to put anything away again.

Simplest answer: it enables programmers on any variation of an OS to get code. If I’ve got a python requirements.txt, getting those requirements installed is the same on any system I’ve got an appropriate python version. The designers of the languages effectively deemed that an important goal and explicitly put in the effort to include package management, in at least most of your listed cases.