Originally Posted by ThermionicScott

Just speaking for myself, if the only cassette options are 11-X and 12-X, big rings like 50 and 53 create top gears that I'm never going to use. Why waste room on the rear axle with cogs that never get touched? Shrinking the big ring makes the whole cassette more usable, and allows me to stay in the big ring longer before dropping to the small ring.