That is why it is in writing. Otherwise it is an ethical violation under Illinois RPC 1.5(e):
(e) A division of a fee between lawyers who are not in the same firm may be made only if:
(1) the division is in proportion to the services performed by each lawyer, or if the primary service performed by one lawyer is the referral of the client to another lawyer and each lawyer assumes joint financial responsibility for the representation;
(2) the client agrees to the arrangement, including the share each lawyer will receive, and the agreement is confirmed in writing; and
(3) the total fee is reasonable.
Who is injured? Conceivably the client. The reason for the rule, I suspect, is that a client may have concerns how diligently the lawyer will handle the client's case if there is a fee split.
I am sure that will appear in these proceedings soon enough.