Marketing mainly is what I would say. They have done an amazing job of branding and product placement / awareness.
Most of their products are good for the price range they are in, and their warranty makes everyone feel warm and fuzzy because you bought a scope for a lifetime. It breaks, you get a new one.
I have used Vortex in the past and most likely will again in the future, personally on some certain optics I am not really keen on using warranty... I just don't want it to break in the first place. Like pistol optics, all well and good getting the new optic but in the middle of a match if it dies I am not to happy so I opted out there for Trijicon. Pinched the pennies and got an SRO.
Same goes for any Precision optics, I would rather be certain that it won't fail me when I need it the most than know if it does I get a new one.
Plinking .22s or some fart around guns why not, I would get a Vortex in a heart beat.