A lot of dev managers like that they can turn one team into two teams by splitting everyone into front and back end. This makes hiring easier. I cannot emphasize this enough. Easier hiring is a huge deal.

As a secondary effect it also allows for more kingdom expansion. It's much easier to have two teams of five than one team of ten.

That being said, I'd rather manage a team of five good full stack engineers than ten average front/back end engineers. The communication cost of trying to get features out the door with two teams of five is very high.