Polk probably would have some worth in a trade, but it would be damaged right now because he is hurt. So a team that might've sent a 4th, might now only send a 5th or 6th because he's injured. At that point, you may be better off just putting him on IR. If you make him one of the two "cutdown day" IR-DTR guys then he can come back midseason without taking up a spot on the 53 for a day.
That said, you don't know if he will be needed by then either. They could optionally just IR him now before cutdown day, use their two IR-DTR spots on other guys, and let him study the playbook all season and get ready for 2026. Two of their WRs likely to be on the 53 this year are in their 30s so there's still a need to continue developing young WRs.
The fact that they have not yet IRed him though gives me the impression that he is a somewhat likely IR-DTR candidate.