because property tax is based on the value of the property, and your property is worth more too?
a different way of phrasing the question: is it fair that your new neighbor pays twice as much as you to support city services, just because they bought their place more recently?
But note that when your wealth goes up because others have driven up the price of TSLA shares you are not taxed on that wealth gain. You are only taxed on the money you get when you sell the shares. If the price of TSLA shares goes to 2x and then later back to 1x before you sell the shares, and then you sell them, you have no gain and no tax.
It is generally considered to not be a good idea in tax theory to tax things that don't involve either money or things that are very easily converted to money, unless perhaps the tax is relatively small. For purposes of this discussion "money" means whatever the government will accept as a tax payment.
That's partly because you ideally want taxes that are meant just to raise revenue (as opposed to for example so-called "sin" taxes) to not cause much change in the activity or thing being taxed.
a different way of phrasing the question: is it fair that your new neighbor pays twice as much as you to support city services, just because they bought their place more recently?