The world is dependent upon Falcon9. NASA gets their astronauts to the space station on this vehicle. The US gets its secret satellites into orbit via Falcon9. It cannot be grounded. The FAA dare not ground it. This is not necessarily a financial attack against Elon. It is a way to diminish his prestige. Teach him a lesson. Ground his most important project. He does has a lot of money invested in StarShip. Probably billions.
Of course it can be grounded. ANYTHING can be grounded.
This isn’t an attack. His rocket blew up. FAA investigated, as they tend to do with things in the air the BLOW UP. And they said “you gotta fix this stuff”, which he obviously knew something had to be fixed because it BLEW UP. This is NOT his most important project. Falcon is the one making money. Right now this is a vanity project that might turn into something useful, at some point, if they stop BLOWING UP.