Say you bought a vintage car -- do you have to pay more sales tax each time the car appreciates? I know some owners of FJ Cruisers that would be pretty upset.
Personally I believe that your claimed cars value is speculative since you don’t mass produce and sell it widely. As a result, it makes no sense to tax you for the unrealized gains.
When you actually find a loser to buy it for the asking higher price then you should be taxed for your lottery earnings.
Some states and countries actually do tax personal property like cars. Virginia and Rhode Island, for example.
In those jurisdictions, if you have a vintage car in 2021 worth $100k, then you pay $100k * TAX_RATE in 2021. If the value of your car jumps up to $200k in 2022 (due to a movie or something), then you pay $200k * TAX_RATE in 2022. As long as the property is still in your possession, you pay property tax on it.