Well, the spreading of commuter style aircraft and regional jets has increased greatly the number of smaller seats. Even as the RJs grew over the turboprops they replaced, the operators stayed with the itsy-bitsy seat widths because they already had people used to sitting in discomfort -- to place normal width seats would have lowered the pax count and their profit levels.

Many smaller airports that had 'real' jet service are now covered by turboprops and RJs, even for durations that are FAR too long for the cramped space. These things are okay for 1 hour jaunts but excruciating for 2.5 or 3 hours at a sit.