From my observation, it has been because the right well-understood their losses in the last political cycle and learned how to empathize with and embrace their disagreements. The "battle lines" of the traditional right/religious right/(multifaceted-)alt-right (as in there's 10x as much political diversity there) don't line up at all and in some cases seem to be mutually opposed (religious Zionists & Neo Nazis), but they all hear each other and give each other a platform. They also constantly debate their politics. They all manage to find some thing or another in common and work to that goal.
In contrast, us (and I strongly consider myself one) progressives show absolutely zero empathy for people that do not agree with our politics to a tee. We're all about "correct thought", focus sharply on how we are divided and shut down conversation with outsiders. Honestly at this point I'm completely disgusted with the movement and the direction it is going.