I've actually noticed at the two Discos near me that sometimes the Caja Rapida line is often the longest line by an order of magn. of 5 or more, and i often get checked out faster in the regular lines. It's as if there is a blind faith that their line will move faster, despite the fact that the second cashier is on break or otherwise not there.
The real problem is that there is no competitor chain with short waits, and no real demand for one. Until the people demand it by shopping in Chinatown or a more efficient competitor opens and steals their business, things will not improve.
But as many have said, it's part of what makes living here different. We must simply adapt (or fix the problem ourselves, hahahaha).