I'm not sure, but I think most of the LE units that still have spike hunts started out as spike only units, until they got enough large bulls to start harvesting them as a limited entry unit.
They continued to allow hunters a chance at spike bulls during the later general elk hunt, but allowed mature bull harvest during the rut.
Unfortunately, it has become a big problem for LE archery hunters because spike archery hunters can also hunt in the same place and time as the archers who have big bull permits.
I work with a guy who had an LE big bull tag on the Central Manti Unit that had to battle with spike hunters. He said every time he got in on a big bull, some spike hunter would mess up the stalk by trying to sneak into the same herd. He eventually came home empty handed. He could have shot smaller bulls, but he expected that he would have a better chance at the big bulls.
As an archer, I would be very cautious about putting in for a big bull tag in a unit that also allows spike hunting because of the competition.