Obama couldn’t handle it. He pressured Perez, who was musing about running for governor in Maryland, into the race, and bore down on the establishment to break with the Ellison unity shtick and accept his preferred candidate. This eventually succeeded, with the help of a party coup in Puerto Rico that delivered Perez all of that delegation’s votes.At the time all the Serious Politics Knowers were like "oh, well, Perez and Ellison are exactly the same so the Bernie Bros are totally stupid for bothering with this unimportant thing which no one should care about oh why is this the one thing Obama himself is getting involved in hahaha SQUIRREL."
Obama, now a movie studio boss and occasional public speaker, had no personal reason to force Perez on the party. The most logical reading of his rationale would be that he did it for the blob, the network of consultants, strategists, pollsters, lobbyists, policy mandarins, and media figures for whom politics is their business. They didn’t want the spigot to close on the hundreds of millions of dollars that flow through campaigns, and they needed to eliminate the threat of a gatekeeper like Ellison, who might have different ideas. So Perez was installed.
Too much is explained by the fact that too many people need a third boat.