Earlier quoted context omitted.
Is this a guess? Do you have any evidence of “secret offers”?
There are a number of writers who have disclosed their “offers too good to refuse” from substack, including their first big name who they paid well into six figures to jump platforms.
What you're describing sounds like a cash advance/guarantee which Hamish mentioned about 'de-risking' offers.
If you have good data that a writer could make X money, but they're afraid to leave their day job - it's easy to just say to them "we'll pay you your day job salary to de-risk this jump for you" if you know they'll make way more than that. You can even offer more.
That's not a 'secret benefit' to prevent them from leaving - it's a smart economic move to help people anxious about perceived risk.