Astronomy isn't limited to the US and the NSF is not the only funding agency in the US. Sure, the annual cost isn't $50B/year, but that's a shitty metric to use, it is textbook tragedy of the commons.
It properly captures what populations, acting through their governments, think of the importance and value of astronomy.
It doesn't capture the value of individuals looking up and seeing stars. But I suspect the continued migration to highly illuminated cities shows that value isn't very high either.