they simply penalize people that try to hoard dollars and not circulate, via tax and inflation
so it doesnt matter to the government that rich people borrow against appreciated assets, if they spend the borrowing then vendors sell stuff and also pay tax on that. if they pay interest the bank gets that, usually. if they donate the loan proceeds or the assets thats fine too. if they invest it thats fine as well.
obviously almost no individual politician perceives it this way, and a law may be passed through their house, but the aggregate outcome is that risk and money circulating is incentivized by not being taxed, accumulation of just cash to hoard is disincentivized by heavy taxes.
which is palatable because the masses of working poor only relate to taxes on transactions categorized as income instead of everything else that rich people actually use