A painting can be valued. A vintage car can be valued. A movie script can be valued. My house's value changed a bunch during COVID; I'm still taxed on it! Each is an asset; none of these examples can be perfectly valuated; each may see its value change dramatically over time, but you can still estimate its worth pretty well.
Hell, I can put my house address on Zillow and get an estimate in real time.
Valuing assets is a routine, widespread thing.
You can't just handwave away the fact that the real world exists.