Tim for me it was the size.
I'm a tall bloke, used to carrying gear, but I wanted a camera I could easily hold one hand, was water resistant, interchangeable lenses, efv.
At the time Olympus EM5 filled the list and I've never looked back.
regarding mirrorless cameras and why they are considered superior to a normal camera
Some may argue that way, I wouldn't venture that track.
That's a Pontiac versus Oldsmobile, Holden versus Ford one, or whatever make you put in there IMO.
It's obvious new cameras draw some like light attracts insects but that's no different to other bits of technology.
If you're hunting for a camera then look and get what suits your inclinations in the photographic area.
To answer your question, I'm not sure there really is any one defined answer.