I really prefer apps.
I can remember a few times turning up to something like the York chocolate attraction to be told the next available slot was the next day, when we were only there a day.
At least with booking online, you can avoid wasted journeys and disappointment when something is full.
As for early booking for Christmas attractions, it's always been that way, long before apps. About 20 years ago, we wanted to take our toddler son on a "Santa" special train at a nearby steam railway. Thought we'd be fine to book in November, but when we phoned, they said all sold out and that they opened the bookings in August and recommended we phone the day the phone booking line was open otherwise they sold out within a couple of days! That was 20 years ago before apps!
Even where app/advance booking isn't compulsory, I still like the option of being able to book in advance to "skip the queue" as I've always hated having to wait in long queues whilst people in front are faffing around wanting advice, not sure what ticket they want, faffing around with payment etc. So much better just by passing the (usually stupidly long) queue for tickets and going straight to the entrance, showing an app screen or paper printout for them to scan and going straight in.
Always hated that at places like drive through safari/animal parks where there were always long queues of cars, each one seemingly taking forever to pay etc. The last time we went to Knowsley, it was all pay by app (year after covid) and even though there was a lot of cars going in, it was so much quicker as the staff on the entrance were just scanning screens/printouts, so barely any queue and barely any waiting, even though it was just as busy.
As others have said, there are more people than ever going to these attractions, etc., so timings etc have to be managed. It's bonkers for something to be full to capacity between 11 and 2 when it's quiet 9-11 and 2-5 - by making people book in advance, they can spread the number of visitors over the day. Lots of people thinking they'd get somewhere at 11, can easily get there at 9.30 instead if they know in advance they're the only slots left.
It was like this pre covid too. We went to Barcelona around 2018 and had to book a few days in advance for tickets for Park Guell - we'd been looking on line for a few days and saw that it got booked up 2/3 days ahead, so when we knew which day we wanted to go there, we got it booked. When we got there, loads of people trying to book at the gate were being turned away and told they were fully booked for the next 2/3 days - lots of disappointed people. When we got in, it was still heaving with people - full to capacity!
Same with the Anne Frank House. You can't book in person - they have no booking/ticket office. It has to be done by app, and you're looking at 4-6 weeks ahead due to massive demand and, obviously, it's a small house, so visitor numbers have to be limited. It took OH about a month of logging in every day to check if any places were available. Finally got some for the afternoon of our last day in Amsterdam, just managed to squeeze it in before going straight to the airport afterwards. Well worth it though. But again, this was long pre covid.
When demand is so high, you can't just be turning up on the day and hoping for the best. With population growth and more people wanting "staycations" etc., it's inevitable that some kind of "rationing" and control of entries is required for popular attractions.