What the government could do is stop loaning out money at 0% (i.e. printing free money which inflates assets, like stocks held by wealthy people). If the prime rate increased, the rate banks would charge on asset-backed loans would also increase, which would make it less attractive than just selling the asset and paying the capital gains tax.
That's now how borrowing money to buy a house works.
Anyone can start a company tomorrow and declare that they have a billion shares of stock in that company. They only become worth something because the person that started the company uses their own effort and ingenuity to make the company do something that is valuable to everyone else.
Taxation isn’t necessarily based on what’s fair or rational, it’s a way of financing public expenses. It might be more logical from the perspective of the people as a whole to tax wealth more and income less (for example) even though wealth is less logical and “fair” to tax than income or consumption.
When you get a mortgage to buy a $750k house, do you want to be taxed as though you had $750k income that year? You’re just borrowing against the value of an asset after all.