I think that the way Genie+ changes touring styles probably has something to do with it. For example, imagine Suzie Q Mom, planning for her family of 4. She decides to rope drop Frontier Land in the morning, hotel break with naps midday, and reserve her three fast passes for the afternoon. She wants them all in the same area of the park, so she manages to get 7 Dwarves, Pooh, and Small World. She decides to skip Peter Pan unless she seems an unusually short line around parade time, and go ahead and wait for Little Mermaid, Dumbo, and the carousel, because those are low wait times. She has an ADR for an early dinner at Crystal Palace that she knows won't conflict with her Fast Pass times. After dinner she might casually try the "refresh" strategy to see if anything good nearby pops up, but if not, no sweat, she has a good day on the books already.
Now look at Suzie Q Mom with Genie+. If she wants to rope drop, she literally has to start grabbing Genie+'s at the same time, if she chooses to use Genie+, because there is no option to just reserve times in the afternoon. So maybe she wouldn't have worried about it in the morning at all before, and saved her precious three Fast Passes for the afternoon, but now it makes no sense not to go ahead and grab whatever comes up. She gets a Genie+ for Thunder Mountain at 10:00 and rope drops Splash Mountain. Now it's 10:30 and the park is filling up. What makes the most sense, from her perspective, is to look for a short line and to go ahead and grab whatever Genie+ is available. Even if it's not what she really wanted, it's something, right? She zigzags across the park and gets a Genie+ for Little Mermaid and then does a short wait for the carousel. She probably would have waited in line for Little Mermaid before but, whatever, it was the only thing available, and she has this product, so it wouldn't make sense not to use it. She sees a Genie+ time open up for Small Word but it's in several hours and conflicts with her ADR. Frustrated, she uses Genie+ one more time for the Teacups even though no one really wanted to ride that, waits in line for Philharmagic, and goes back to the hotel, still scrolling for Genie+ times for the afternoon. The only thing that comes up is Tomorrowland Speedway so she takes that. By that evening all of the Genie+ times are gone and she can either wait in long lines or choose all of the less popular rides.
FastPass changed people's touring, to my mind, because:
- Your three "locked in" FastPasses were precious, and there was no incentive to overlap that with rope drop. To the contrary, it made more sense to skew towards the afternoon (a few people were so confident of their refresh skills that they wanted to use them all early, but not for most people). Now the opposite is true - you have no option to reserve times and you know Genie+ times are getting taken by other guests every second you wait, so everyone grabs what they can as early as they can pell mell.
- People with FastPasses later in the day couldn't start refreshing, and even if they could, a lot didn't think to do that. Many had already had the day they wanted to have anyways or didn't know about day-of Fast Passes. Genie+ is designed so that every single user is incentivized to get what they can when they can, so there's a lot of incentive to take a "whatever, it's better than nothing" ride. If you can wait thirty minutes for Little Mermaid in standby or twenty with Genie+, well, better than nothing I guess.
- Knowing when their FastPasses were encouraged people to fill in the gaps with other things, schedule-wise. "Oh, no FastPass then, let's plan on a snack / show / break / etc." A lottery system where you never know what might pop up when incentives people to be "on" all the time, always on the hunt for what might pop up.
Just my theory, anyways. I think this is a big part of the reason for limited availability.