Size in a way, as well as convenience...I know leather strops should not be stored rolled up for any period of time and my travel bags are pretty compact, not conducive to accomodating a laid out (or somewhat curved) strop inside. Also, often I travel by motorcycle and believe me, a strop and Harley saddlebag do not interface all that well.

Plus, I'm trying to accomplish this on the bargain side. Don't want to pony up $$$ for a kangaroo strop.