In short, BYU has to make them pay for focusing on Bushman. Then they'll focus elsewhere and he will get the ball more.
The O has been better this year, but still not putting up top stats. Double teaming Bushman has worked out OK for opposing defenses so far, with few points scored in regulation. If the BYU Offense was killing their opponents by successfully throwing to all the other receivers, throwing for 300-400 yards per game and running well with T'yson, Esukpa, etc. then the defenses would have no choice but to stop focusing so much on Bushman.
I haven't looked at the stats, but I wonder how the total offensive output from that 1996 team (one of the best BYU teams ever) compares to this year's team? Or was the 1996 defense just that much better than this years team?