In addition to what @twoinanddone has stated there are certain practice areas where firms have to be approved by the large corporate clients for ongoing work. That means our firm is approved. As soon as the firm is sold the new firm will have to get on the approved list. It isn’t always easy for the new firm to be approved, especially if there are conflicts between clients.
Law firms have little (to no) value beyond the value of the assets. The value of the firm is in the client list but the client list is only valuable to our firm. We have had lawyers unable to join the firm because their client list and our client list are incompatible. We have had to turn down some RFPs because of our existing client list. We get referrals from other firms because they can’t take some clients due to conflicts.