In the CFL and AAF aren't getting paid well. And only the very best make NFL rosters. Minor leagues are huge and full of guys drafted straight out of high school. NFL stashes them in college where they aren't paid well. Both the NFL and MLB are the best of the best.

A top 800 baseball player makes more than a top 800 football player.

And to the point of Kyler Murray, he had a $5 million bonus from the A's and 70% of first round picks make an MLB roster. The percentage for top 10 picks is 82%. His NFL contract will be higher, if the Cardinals or someone else bites and he goes top 20 otherwise he's looking at a contract with the same or lower guarantees. No guarantee he makes more.