It is fundamental to the tax code. Say someone gets paid some amount of gold, holds on to it for 10 years then tries to barter it for something.
They'll get charged with tax fraud on the theory that their lump of rock is worth more now than it was when they bought it so they should be paying some amount in capital gains tax.
Now I'll accept an argument that we should have some sort of transaction tax, fair enough if you want to believe that.
But the theory that the gold is becoming worth more over time in real terms is blatantly silly. It doesn't change, the supply of gold is increasing faster than population and the arguments that its value is changing are frankly a bit forced. It isn't increasing in real value at a rapid rate like the official numbers suggest it is.
And the US dollar is, by policy, losing value - so the same basic argument will hold for any asset even ignoring the fact that the inflation numbers are wilfully ignoring asset price inflation.