Because taxes are theft. There's no reason for them to maintain the illusion of justice because at the end of the day we pay taxes because we have to, not because we want to.
Also, inflation is just another tax, but it's a hidden tax. They certainly don't want to do anything to draw attention to their midnight robbery. Making it a legal tax code issue would open the government up to lawsuits about how they report inflation, and that would risk exposing how much they lie about the true rate of inflation. Which would mean more COLA on Social Security and less revenue from capital gains taxes, all of which is the opposite of what the parasite class wants.
And the fact is, most capital gains are just inflation anyway. That's the whole purpose of the tax. You invest in assets to avoid the inflation tax, but they can't allow that so they punish you by taxing you on the inflation you tried to avoid.
No, the house you bought 20 years ago that needs a bunch of repairs and constant maintenance now isn't an "investment", and the massive increase in its price isn't a gain in your capital, it's just inflation.