The problem is nobody else compares the rounds in identical guns. I do. I own a 36 oz all-steel 1911 in 9mm and in .40. The recoil on the .40 is maybe 30% more than the 9mm. I also shoot (don't own) a 1911 of same size and weight in .45. Total recoil feels to me about 50% more than the .40. I don't like the long slow push of the .45 because it makes me wait to follow up. Shoot a .40 in an all-stell 1911 and it is a dream. A nice quick pop and then back on. BTW, My wife also loves the .40 and hates the .45.
The bad rap the .40 is getting is because most of them are light, small guns like Glocks or Hi-Powers that tend to flip the nose up anyway. Put it in a real gun and you'll like it.
BTW: the answers to the question why is the .40 becoming so popular:
1) It is perfect for LE use, and is the descendant of the 10mm which was developed specifically for LE. Compared to .45, the .40 gives more round capacity, lighter weight and stopping power about dead even with the .45 (no flame wars, just reporting the data).
2) .40 ammo is a lot cheaper than .45. I can get FMJ reloads in .40 for $122/thousand and .45 ammo is way more.
3) You can get single stack (flush) mags in .40 with the thin followers that hold 9 rounds which is better than 7 rounds of .45 for capacity.
4) My bad back complains if I had to haul 200 rounds of 240-grain .45 ammo to the range as opposed to the 180-grain stuff in .40.