Two major points: MUCH lower bore axis which reduces muzzle flip and the same trigger pull all the time. This makes much more difference that you realize. The effort the trigger needs was also a very nice compromise between the initial weight of the TDA trigger and is/was very close to average out of the box SA weight. The trigger qualities that you despise didn't make any difference in practical terms. In fact, average qualification scores went up. I was surprised at how many went out and bought their very own M&Ps after experiencing the issue pistol (although some chose different calibers/versions).
Come to think of it, the M&Ps adaptability to hand size and reach to the trigger is much better than many of the 3rd generations. 3rd generations using the 5906/4006 frame needed massaging with a Dremel and a grinding wheel to eliminate a sharp edge near the magazine catch for many people.
I happen to have personal experience with "quality" triggers of various types. I can relate to your preferences. The major point being, as a service sidearm, those qualities aren't significant.
Finally, S&W needs to stay in business. In order to do that, they have to make money. Someone mentioned price above. When the 1000 series went out of production, we had to add 4006's. When we couldn't get 10 mm ammo in sufficient quantities, we got a quote on 4006's to have everyone with one. When the sales rep showed up with a pair of M&P's, the reaction was a groan. After a whole bunch of us shot them the reaction was: "When/where can I get one!" (the two sales samples were bought by firearms instructors/armorers) We bought everyone a new service pistol and web gear for what the 4006's would have cost. Possibly with a few bucks left over.
I do know the .357 Sig version wasn't a success and isn't in production. Nor is S&W advising conversion to the caliber.