When a thread in ANY part strips out, there's usually one of a few things to look for..

Biggest one: over torquing (tightening, which boils down to people having gorilla hands, and not knowing their own strength)..

Second : A low percentage of cut thread (thread depth, peak to valley) in the part. This comes from the tap drill selected being too large.. Standard thread cut is approx 65%. Less than that, and you begin to really run the risk of easily stripped threads from not enough thread "overlap/contact..

Third: Worn cutting tools.. IE: drills cutting oversize, worn taps..

Just a few of the majors to consider. Most people will NEVER admit to stripping out a tapped hole, because they don't know what it feels like when the threads give out and strip.. They usually fail after repetitive over torquing, and give way quite easily so it's usually hard to feel it let go..