He still was not the #1 receiver, and even though Keyshawn may not have had the abilities that Owens has, he was still a very servicable WR and demanded attention his way. Even during Glenns fabulous 2005 season, he was shut down and often frustrated when the defense focused their main attention his direction. He was not as successful when doubled or when a safety was over the top. However, he excelled when he drew one on one coverage or was matched up with the nickle CB in the slot. Owens draws double coverage and has a safety over top nearly all the time, yet managed to put up top numbers.
I didn't say it was THE reason, I said you could argue that reasoning, and it is a very valid argument. The question still remains: Would Glenn be as productive as the go to guy with a lesser WR playing the #2 role? Would he be as productive drawing the attention of a #1 reciever, being doubled play in and play out? Recent history indicates that he isn't as productive when double teamed, so he needs someone to take the pressure off and use his advantages against man on man coverages.