Well, to correct things a bit...
40S&W wasn't the first. There was the 41AE which did everything the 40 would later do with more power in the same size with the rim of the 9mm. But, Action Arms lacked the panache of S&W, so when the 40 came out, that was that for the 41AE. In any case, the trouble was that the 10mm was being down-loaded for the FBI, which made no sense to keep the long "magnum" case for the round, so the 40S&W gave the FBI performance in a smaller case.
.45GAP wasn't first in its concept, either. The South Africans did it first a few years earlier with the poly-framed .45 Truvelo. It was the exact same concept, a 45 caliber round in a smaller frame. The Truvelo pistols were later picked up and manufactured by Wilson Combat as the ADP as well as Heritage as the Stealth. The GAP wasn't the first, just a Glock copy of the South African product.
In any case, the GAP was a failed idea because few people really wanted it before hand. 9mm and 40S&W guys already had their pistols and were not pining for something bigger. Big bore guys had their pistols and were not really lamenting the lack of smaller grips. There was grey area where some griped, but that was a small market. When GAP came out, a few vocal supporters trumpeted the end of the ACP. But, why would all the ACP owners scrap their pistols (in platforms they really liked) to adopt a new caliber? They wouldn't. With the vast numbers of 45acp firearms out there, ACP was secure. Would the 9mm and 40S&W guys trade out theirs to get the GAP? No again. So, it was limited to expanding the armories of those who already sided with 9mm/40 or those who liked the ACP. As mentioned, few really wanted to go up or down, depending on the preference, and that left a very small market, really, for the GAP. It plays second fiddle to both the 40S&W as well as 45acp in power.
And, the large number of detractors was itself evidence of the gaffe Glock made. Not enough 9mm guys supported it (other than its being the size of a 9mm pistol) because they were already convinced in the superiority of their round, and in 9mm you STILL get more rounds in the magazine than GAP. Not enough ACP guys supported it because, well, they had their platforms and had no need to change. Some lamented the fact that ACP guys wouldn't roll over, but why should they?