I liked him too, but I'm guessing the team views him as a WR3/4 and that a cheap player already on the roster can fill that slot. Agholor, Meyers and Bourne are, currently, your top 3. After that, it's up for debate who your WR4 and WR5 (assuming they go that deep at WR) are...
Harry? If the team doesn't trade him before TC, I think they'll give him an honest shot to improve. If they don't see enough, I figure they'll flip him to the Texans for a lower round pick. Better than cutting him outright.
Gunner? I think he's a near lock to make the roster just because he's a good PR and probably the Edelman heir apparent. Plus he can play DB in a pinch (probably).
Nixon? Seems unlikely since he was a 7th rounder, but he is known for "getting open" and has speed (4.44 forty) and a decent 3-cone.
Zuber? I'm biased since he was my '20 binkie, but I would love to see him make the team. Has great size and shows really good body control in his college tape. Had a couple nice end-around plays last year.
Wilkerson? He spent a year on the PS and seems to have the physical makeup to be a good reserve WR. IIRC, he was at the Stidham-led Patriots passing camp and looked pretty jacked.
At the end of the day, they probably figure even if none of Harry, Zuber, Nixon or Wilkerson step up, Gunner is probably "good enough" to be the 4th WR. I really doubt they run many plays with more than 3 WRs anyway... you figure most plays will only have 2 WRs, honestly.