To do this legally, one can have a separate legal entity to hold on to third party assets. In the Netherlands this can be done using a foundation (stichting derdengelden).

Any transactions of third party assets go through this entity and don’t touch the company at all. And this entity doesn’t take on any risk, whatsoever.

Fees etc, of course, happen separately and are paid to the company.

So in closing: this has nothing to do with fairness and everything with the exchanges (whether purposefully or through negligence) not working this way.