Or stick around your final year and get a NIL worth more than what you'd get paid as a fifth rounder.
Every situation is different, of course.
Aaron Jones was a fifth-round pick, he's doing alright for himself. I realize you said that every situation is different, but RBs aren't typically going to be selected in the first or second round much anymore, majority start coming off the board in rounds 3-5. In the last three drafts, only four RBs have been selected in the first round (2 in 2023 and 2 in 2021; 0 in 2022), only five have been selected in the second round (1 in 2023, 3 in 2022, and 1 in 2021).
So, you say go ahead and risk season ending injury, and put more tread on the tires, for a one-time NIL payout that won't be as much as a 4-5 year rookie contract?
Majority, if not all, of these projected 3-5 round RBs are top 10 at their position, so these teams are likely committed to them as RBs of the future. You can make an argument that a guy being drafted in the 6th or 7th round might not have a secure roster spot, but what kind of NIL would they be making to return to school, anyways? The reality has set in for RBs that if they get a mid-round draft pick, that's basically saying it's now or never for your NFL career.
There are only a handful of players who could realistically improve a "mid-round" grade into a top 65 selection, given the fact that only nine RBs were taken in the top 2 rounds the past three drafts combined.