Ok here's the deal. His production is less than his rookie year. He is on his 5th year next year, cap at ~8.5M or so. Carolina has ZERO cap room. They drafted a guy this year who's just like Kelvin Benjamin BUT is actually better, and cheaper.
KB also has issues - speed, undisciplined route runner. Doesn't work on his craft in off-season.
but he's a big guy, 6'5" sure handed receiver. Basically a tight end in WR position. I think Tyrod likes those.