The reason is weiner envy. Glock are $500 and not flashy, they require good skill to use at a high level. There’s nothing really different between a m&p and a Glock in terms of competability other than maybe the Glock is a little more robust and the m&p is a little more “feel good” in the handI am honest about my carry weapon, and it will never be a Glock.
I compete with an M&P in matches. If I thought a Glock would serve me better by being more reliable and better handling, that would be the firearm I’d compete with. Very few match competitors use glocks. There has to be a reason.
I carry what I compete with because the controls are totally familiar and requires nothing for adjustment.