People are willing to pay additional money in the hopes of actually being able to ride attractions without spending their entire day in a theme park staring at a phone, constantly refreshing, and hoping for a lot of luck.  For guests who don't want to preplan extensively, wake up early, or are foolish enough to stay off-property, that's the alternative.  In one scenario you're paying extra to ride, in the other you're wasting the amount you paid for your base ticket by anxiously staring at a phone with absolutely no guarantee of success.
The entire scenario is garbage.  Idiotic line-skipping systems combined with chronic, egregious underinvestment have turned the WDW experience into something miserable.  The only way to begin to fix the parks is a massive expansion campaign coupled with a return to stand-by only (or a line-skipping option that is so expensive the vast majority of guests opt out).  That isn't going to happen.
WDW has created a situation where the only way to win is not to play.