What you seem to fail to recognize that business is primarily about relationships. You get jobs from previous clients, previous clients who moved to a new company and the recommendations from previous clients. The relationship with a client is largely based on performance and trust. You don’t build trust because you “have to”. You build trust because it is in your best interest.
Because you are getting a kickback.
Either a Client is paying you for sourcing, or they are not. If they are and you get a kickback, they are paying you twice for the same service, also called double-dipping. If the Client discovers that, you will never do business with them again.
If the Client is not paying you to source but you do source, it begs the question as to why. If the Client needs to ask why instead you explaining why, again, you are likely lose their business. Even if you are sourcing for the reason to go above and beyond on a project, there is no “commission”, if a Clint needs to ask, why would they trust your answer?