When the M&P came out with the manual safety it may have been to get sales in California. (Large population) and most of the prospective buyers not understanding the DAO trigger is a safety.
For over a hundred years LE officers from local to federal carried revolvers that had no manual safeties.
For serious SD situations that happen in a few seconds pointing and pulling the trigger is all there is.
Glock is one of the examples in that there aren't any manual safeties.
Many folks want to change a designed for SD situations pistol and want it to be their range pistol, so start making changes. I've carried for sixty years. The first 24 LE. No manual safeties during that time.
G'luck and stay safe.
PoliViejo