Getting back on topic, the reason the boys mother is more involved in a boys shidduch, is simple. The boy and his parents are looking for a wife. This means talking to the teachers, friends, neighbors of the potential kallah. So who is going to make the phone calls to the teachers and friends etc. the Tatte or the Mamma??? Obviously the Mom!
When looking for a Chosson, son-in-law it’s the father who will be making the phone calls to the Rosh yeshiva, roommates, mashgiach etc. SIMPLE.