Rainboe,
Good question, and I hope somebody well-informed can fill us in on the background.
My first reaction was "weight"....
"Hydraulic" is now a "mature" technology, and you'd need a breakthrough to significantly bring down the weight.
"Electric" is still evolving, with new materials, more efficient switching and control electronics, etc.
So possibly the "cross-over point" has been reached, where tossing out the entire hydraulic system and replacing everything, even the "big" stuff, with electrical systems, allows you to bring down the weight enough to make it worth the effort.
Happened years ago on choppers, when we started replacing hydraulic flying control actuators (autostab, autopilot) with electrical ones.