Roll crimping allows maximum volume for the load (powder, wad, and shot) for a given hull length (fired length!!). Both the 2 1/2" and 2 3/4" hull lengths existed before the rise of star/pie crimping. To match the usual 2 1/2" loads with a pie crimp shell it was "necessary" to go to the 2 3/4" hull, but not to load the heavy loads they have volume for if roll crimped.
The use of known low pressure pie crimped loads in 2 3/4" hulls in 2 1/2" chambers is well documented. If the load is of "low" pressure, there is no objectionable pressure increase from the 2 3/4" crimp opening into the forcing cone of a 2 1/2" chamber. This was well documented at the time of introduction of 2 3/4" pie crimps as more or less "standard" fare. Unfortunately, said documentation seems to have fallen out of common/street knowledge. The advent of interest in shooting Brit/Continental game guns has led to the rediscovery/reinvention of this knowledge. Always keep in mind that SAAMI (USA) loads allow higher pressure than do CIP (Europe). The taboo of 2 3/4" shells in a 2 1/2" chamber has, or at least should have, more to do with the higher allowed SAAMI pressures than with the hull length difference.
DDA
