because as a whole they're not very good?
Wells is undersized and cannot get off a block. Bohanna seems to be out of position fairly often and doesn't get off blocks. Skinner is OK but seems to disappear on plays. Hughes ever make a play?
McKinney is a bright spot and even he is currently a B+ rated SEC type LB. He will grow in to a solid one though.
You are forgetting about the 2 4*s that we redshirted and bulked up this year. Both are 4.4-4.5 guys at 225-235lbs. Richie Brown will be better on day 1 than Cam Lawrence was on the day he left here IMO, at least athletically and in coverage...
Also, Wilson's read and react scheme KILLED our linebacker production. Looked much, MUCH better in the bowl game with Collins calling plays and unleashing them a little bit. Our DL was so terrible that the OL was blocking into the second level quite a bit.
I look for LB to be the overall strength of our team next year...