But they can do a lot to destabilize. The US never formally invaded Libya, either.
Problem is US doesn’t want to destabilize the sahel region too much, since the junta is not targeting the statesians, but only the french are the ones truly being humiliated. Sure they’ll support as many rebels as possible, but this isn’t a libya situation, since libya got completely ganged up by not only the europeans/americans, but all their neighbours too, it isn’t even a syrian situation either, since all of niger’s neighbours have just recently signed a military alliance, and anti-terrorism shared agency. And niger lacks the political powder keg which was present in these nations.
The french are forever gone from this region, they’ll never return, and there really isn’t the same criteria for some overthrow, since the junta enjoys wide public support.