it's already a black hole for funding
Said the grumpy grandpa, shaking his hand at the cloudy sky. I dont know what value that comment contributed, funding research is always a long shot. And often times it fails, but that is kinda its purpose, we dont know what we dont know.
With the LHC there was a very clear goal: verify the Standard Model and prove (or disprove) the existence of the Higgs boson - and hopefully discover some unexpected stuff along the way. On the other hand, the FCC is mainly a shot in the dark: they aren't validating a widely-accepted theory, they are just hoping that if you spend enough money on a bigger collider something interesting will fall out.
Most research gives you at least some insight. With the FCC there is a very real possibility that the insight will be "our $20B collider found absolutely nothing, now give us $1T to build an even bigger one". Sure, funding research is a long shot, but at a certain point you're just setting money on fire.