But the NFL is a union shop, right? And rookies are on a 4 year deal with mandated salary levels? Otherwise all the studs would do what you said.
A walk-on must sit out one year of eligibility if they believe they will be drafted by a team they do not want to go to........Some have done it in the past, but is is a risky move............
Here’s a good article That has some info I wasn’t aware of:
https://www.si.com/nfl/2019/05/14/nfl-rookie-contracts-sacrifice-pay-negotiable-terms