Blank adaptors dirty up a weapon in a hurry. I don't know if you've had military experience, but I remember awful days of cleaning an M16A1 (that's how old I am), just to get it rejected time and again by the armorer, before I could turn it in and go get a beer.
After a while, we learned to spend weeks in the field without firing a single blank. We'd just yell BANG BANG instead. Yes, it's silly, but at the end of a training excercise we'd be sipping a cold one while the rest of the guys were up to their elbows in CLP.