My training and experience has taught me that if something goes wrong with a QUALITY, WELL MAINTAINED semi auto handgun, it is most likely due to faulty ammunition, or faulty magazine, or operator error. I carry two spare magazines because that is how I was trained. Not because I am likely to need to shoot that much, but to get back in the fight if I have a failure with the magazine or ammo that's in the gun. Think of malfunction clearance procedures. If tap, rack, bang and slide manipulation doesn't get you going again, dump the magazine, reload a new magazine, and start over. Absent a reload on your belt, you are reduced to a 2 pound club. I would also invite you to consider that after you have dealt with an aggressor, he might have confederates on the sidelines who you have to deal with next. We just don't know what the future will bring.
I will add one thjng I have observed and Daryl Bolke (who has been in several shootings if his own and investigated several of his own agency) and John Hearn had mentioned it in depth whem we talked (of you don’t know who Daryl Bolke and John Hearne are they are pretty relevant in the teainjng industry so it’s more than a coulke random guys talking about what they heard)
Another issue is poor grip. In a large number of the stoppages in LEO shootings is whem they are surprised shootings where the Officer is startled (rightly so) and doesn't get a great grip on the handgun this has been recorded in video as well as officers testimony.
There are other issues we could go into but just a quick add
And as far as weapons being serviceable that can play a huge part and an example that I sort of chuckle at is as the whole a lot in the industry (usually guntubers that have never been in or interviewed anyone in a use of force situation) down on 1911’s while they won’t get through a 1,000 round 2 day class without maybe cleaning like a Glock can without if it’s in proper order it shouldn’t have an issue getting through say three 8 round mags without issue