It's pretty simple. A lesser quality optic does not have the same quality parts or attention to detail or quality control an expensive one will. Some people get Lucky, and get one that just works. There are good ons and bad ones with everything. Vortex is ok, but why would they make their razor line if the cheaper viper line can track the same. My experience with 2 of this same scope on the same rifle is that they don't track well. And of the 2, one was no better than the other.
I've got a Viper PST with illuminated recital, its a nice scope but I DO agree with Tchardy you do get what you pay for !!! All my hunting rifles have Ziess optics and except for 2 that have 4200 elite Bushnells . The Vortec is on a target rifle its ok but to get the cross hairs to illuminate you gota tap the cap where the battery is to get it to make contact and work ( EVERY TIME :-(( ) , I also find at longer distances ( 300 yrds ) at our range its very hard to focous, and keep it focused . For the range its probably more than enough but in a competition or for the serious hunter I want something way more reliable. I've learnt that you might as well save up a bit more and get something real nice and reliable vs middle of the road or bottom of the barrel ! I've owned Sightron scopes as well and personally found them to be about the same quality as a Vortex. I personally wouldnt buy either 1 again.
Maybe thats why Vortex has the warranty that they do , it makes a great selling feature!!! Suckered me in LOL !!