The more you go, the more you value flexibility. You can make changes on the fly because you don't really have any must-dos. Must-dos become "would be nice to do, but if not there's always next time."
I think this is true. When you've done every attraction hundreds of times, your tolerance for line waits is far less, and your desire to schedule yet another ride is even less.
If a casual visitor pops down to Magic Kingdom for the afternoon they might in the past have, for example, met up with some friends and been walking past Buzz Lightyear, seen the standby line was only 10 minutes and decided to ride it. But nowadays, the line is always 45 minutes. So that person goes to the next ride that in the past had a short line, but same again - it's past the threshold. Try another ride? Same again, and so on and so on.
Pretty soon there's nothing left in the park that doesn't involve a long wait. That wasn't an issue in the old days - In the past, even on crowded days, if you were with a group of friends you'd walk past the ride, see the board telling you what time Fastpasses were being given for, and if the return time was fairly soon and enough of the group wanted to go on the ride, you could all go to the machines and get your tickets.
Now, there is no board to walk past, so at every ride you might want to go on you then have to have every person in your party power up the app and see if you all see the same availability. Or you have to cross the park to wherever there is something with availability.
But will you all see the same timeslots? Probably not. The software has no idea that five parties of one and a party of four all want to ride together, as the system has no way to group people temporarily - it's all done based on vacations, or families, or other groupings that don't fit casual visitors who just want to go on a ride together with people they only know very casually for an hour or so.
Now what if someone in the group has run out of battery, or doesn't even have the app? Well then they need to line up for a kiosk, while everyone else waits, and hope that by the time she gets to the front there is one time that will work for all the groups involved.
It's basically taken what was once a quick, easy and fun thing, and added tons of steps that make it a real chore and not worth bothering with. The reality is now casual groups just don't use Fastpass at all for the most part as it's too much hassle doing all the above, so the waits they experience are always longer than they were, and that's the key reason why casual visitors dislike the system.
