It really just comes down to energy density and the fact that batteries weigh just as much when you land as when you takeoff, whereas you burn off most of your fuel over the course of a jet-powered flight. Those two things together mean that as you increase the size of your aircraft, batteries take up a bigger percentage of your available weight budget.

It's pretty much a smooth curve, with the breakeven point depending primarily on energy density of your batteries. Until very recently, the electric aircraft weren't possible at all. We're now at the point where two seat trainers with short (but long enough for a typical lesson) endurance are possible and in production. If you look at where battery tech is going, we can probably push that up to 8ish seats and a somewhat longer endurance within a few decades. When you look at the size of even a small regional jet, it doesn't seem likely that current battery tech is ever going to get us to the energy density necessary to make it work.