Probably because I don't see Breece staying, franchise tagging a guy that doesn't want to be here is a bad idea. Allen is nowhere near a RB1
I think you take a shot at a back in the 4th or 5th assuming Breece leaves. Hold the fort with Davis/Allen/Drafted RB for next year. Maybe sign one in FA.
I want to see if Davis can start. He flashes a lot. I wouldn't mind seeing Allen play second fiddle in an Alstott role splitting time between RB and FB.