You don't access the money directly. You access loans against the value of it, which, when well-collateralized, have very low interest rates that are more than made up for by the rise in value of the underlying asset.
You don't have to sell shares when you can take a loan out against them instead.
Yes you pay the loan back, just like you would have to save money back up if you spent it directly, if you wanted to get back to the same level of wealth.
If you spend money, the opportunity cost is whatever else you might have done with that money in the meantime.
If you just take a loan out against the value of an asset you have, the opportunity cost is only the low cost of the collateralized loan, because you continue to own the asset and benefit from all its appreciation. AND you don't have to pay taxes on the capital gain because you haven't sold the underlying asset.
I strongly recommend looking into this at whatever depth is necessary until it clicks. This is one of the main differences in mental paradigm between people who become extremely rich and people who don't. It might be counterintuitive at first, but it's a really important, beneficial principle!
You never pay it back if you are rich. Remember a 10% loan would be billions to these people. As long as there isn’t a 90% crash then no liquidation.
It’s not like a middle class refinancing their house to buy a Ferrari and then getting into trouble when they lose their job.
Also: Almost no interest.
No tax (the tax is perpetually deferred, probably beyond death down the generations, although not sure in the US. There are trusts for this in other countries)
$4bn in earnings and $400bn in wealth, it’s more a case of what is this benefit you need with billions in cash?
Is there an apartment in New York whose rent you can’t afford?
What is for sale as a private person that’s worth cashing in the billions and paying tax to buy? You already have a business you can use to turn that into more money anyway which is probably the most satisfying game.