When was the last time you used Atom?
It's definitely not the fastest opening editor, and it does have performance issues, but they tend to be more rare than common.
The 2 that bite me are:
* the update/install screens in the settings tend to be a bit slow
* opening "large" files that have 1000+ characters per line will either hang or crash the browser depending on the size. If it's a "normal" looking source file, it runs like a dream with files up to 5gb+ (the largest i've used it for), but if it's something like a minified javascript file, a few kb is enough to hang the editor.
Outside of those 2 issues, i don't see any lag or stuttering in my normal use, and i've got about 70 plugins on top of the defaults.
But to answer your question, it's the customizability and the massive number of plugins that draws me. Plus it's fucking beautiful, and i know this isn't the most popular opinion, but if i'm going to stare at this thing for 6+ hours a day, i want it to look good!