IDK, I am taxed every year on the unrealized gains of my home. There seems to be a way to make that work.

Sure.

For real property, like homes, every single asset is registered with the local government. That local government has an entire department (usually a county property appraiser's department) whose sole job is to continually appraise and value those assets, including tracking every single sale and the corresponding price. That's aided by a regulatory scheme based on record notice (in most states), all-but-forcing voluntary compliance to disclose all asset transfers. That department also informs the property owners of their valuation, provides a mechanism by which values can be disputed, and defends those valuations in court. The effort involved in doing this is not trivial - here in Miami-Dade County (where I live), the Property Appraiser has a budget of about $60 million and a staff of about 400 employees. Just to fix the valuations of a single class of assets (real estate) for small slice of the population.