I worked for SEIU for some years organizing things like these marches. You do register people to vote at these things, but almost everybody at the march was from the DC area and few of them will actually vote. The radical left's real purpose in organizing an event like this is to find and develop cadre for the Communist Party USA, Revolutionary Communist Party, DSA, etc. I was recruited that way but I quickly dropped out (as do most) as I saw they were lying about everything. They don't care about working people & the poor, they care about their own power.