He gets a large contingent of listeners who support the bernie/AOC/zohran wing of the dem party and would refuse to listen to him if he condemned voting, moves them further left and then directs them to people who will explain why they shouldn't vote dem. imo he's probably a net-negative on the number of dem voters ngl.

Edit: also by being nominally pro voting for the Dems he gets access to a whole mainstream media sphere to talk directly to normie dems about his actual beliefs and is allowed to be far more openly critical of the democratic party on these platforms than he would be able to otherwise