You need to deposit a specific amount of energy into your resin to polymerize it, that takes time as you can't just crank up the amount of charge or the energy

You need to deposit a specific amount of energy into your resin to polymerize it, that takes time as you can't just crank up the amount of charge or the energy / electron in your e-beam as that will usually increase the energy variance and thereby the aberration. It's much easier to produce a coherent beam of light with sufficient energy than a coherent beam of electrons with comparable energy.