Becoming a public company is a way to get equity investment. That is the purpose of the stock market. It was the original purpose of "investment banks" as opposed to "retail banks".
However, that is not what the bankers of Wall Street now focus on, they are more involved in producing "financial products", packaging arcane structures primarily to encourage trading and thus fees from mindless turnover.
Packaging arcane structures and securitizing them has a huge impact on overall risk in the market and enables pretty significant cost reductions downstream (generally) in the markets that can offload the risk via the security.
I understand there are bad actors as well as people making the trades that make money, but there is also an underlying reason the trades get made, typically that is often discounted by your argument and should be factored in.
The reason we can click a button and get a loan is because it is not extremely risky for the company to make the loan, because of said instruments (as an example)
There is a bloat of capital seeking any and all possibility for growth. Even money-destroying companies are going public because growth-chasing has become so desperate.
However, that is not what the bankers of Wall Street now focus on, they are more involved in producing "financial products", packaging arcane structures primarily to encourage trading and thus fees from mindless turnover.