For those who haven't been keeping up, these are huge firms with resources and expertise to take on large federal cases, that have large and diverse workloads that may include things like cases involving classified information. He's extorting them by actually issuing, or implicitly threatening to issue, executive orders blanket revoking clearances for all their lawyers, banning them from federal property(!!!), and blocking any former employees of theirs from being hired by the federal government.

These EOs amount to death sentences for these firms, obviously, and so far they're rolling over and submitting when EO'd against or they perceive they may be EO'd, halting legal work against the administration and providing free labor to Trump.