The issues are more common specific popular days. For example, I could not get one for
Disney+ Day and my cousin could not for the weekend of night shows returning. With the reservation limits, it's not uncommon to need to make reservations within a few days of the actual date of the visit by which point, you may have to check multiple times during the day to catch a reservation. It's often easier to just make other plans rather than deal with that annoyance and uncertainty.
Here's a challenge for you: Make a reservation for
Disneyland start for tomorrow as a keyholder. The reason you're waiting till today is because 3 of your 4 reservations are tied up in future visits and you are in the parks today. You can't make a reservation from 9PM to 9:30PM (you're watching World of Color) or 10PM to 10:30PM (you're driving home) and you'd like to sleep by 11PM to be able to wake up for rope drop at Disneyland tomorrow. How many times did you have to check the site? While this is doable, being annoyed by this process isn't from a lack of research.