RBs these days have a short shelf life. And if Robinson stays healthy through his rookie contract, you’ll have to sign him to a massive extension or let him walk.
This was kind of the same argument on Hock. If he has the potential to be as game-changing as Kittle or Kelce (ha!), positional value doesn’t matter. We see how that worked out, with Holmes deciding he wasn’t worth the contract he would command… while the next guy, Ed Oliver, is at least as valuable as Hock but will re-sign for much less.