Isn’t there a contradiction—if as you say DMCA perjury cases aren’t prosecuted, what’s there to lose for that hypothetical “DMCA troll” LLC?
This hypothetical troll wouldn't have that deniability. It would be very clear that they are knowingly making false complaints.
There’s enough deniability for prosecutors to not care, but there’s also enough evidence that prosecutors could politely inform them that there is a pattern of misconduct.