Moving isn't free, and it can be a burdensome expense. When the housing crisis a lot of people had personal financial issues because divesting from the mortgage they were engaged with and acquiring a more modest property would still involve being taxed on the full value of your house, expenses involved with the mechanics of changing residences, and then somehow affording a down payment on a new place - or else being forced to declare bankruptcy and re-enter the renting market with nothing but fresh income.

The technical concept is that housing is an illiquid asset - there is a friction in converting it to cash, that friction may be monetary (a fee, taxes, a loss of value, sale prices etc...) or it may be time (conversion may simply not be an action that can be executed at will, there may be windows or complex ownership hand-off processes that require weird timing) in the most common cases (including housing) the asset is liquidatable with value generally decrease relative to speed, offloading a property with a fixed window of a month will net you less revenue then having a sale posted for an extended period - having a sale window of a week or less would almost certainly result in a much decreased sale price.

Given the nature of the wealth taxes that have been proposed, you will never become homeless or destitute. Having to pay a few points above 20 or 50 mil or whatever is not going to break anyone the way property taxes will and do.