@Daisyhoney
Yes I agree Kazzyhoward that some places had prebooking before covid - Harry Potter Studio Tours being one - but loads didn't including theme parks,zoos,anywhere National Trust/English Heritage ( we've had passes over the years for all of these and you could just turn up on the day ).
So there has always been loads of places you could 'just turn up' .
Yes, but they were getting fewer and fewer as the years pass. A decade or so again, you would just turn up on the day, for more or less anything you wanted to do. Yes, you may have had to wait. Years ago, we were in Florida and went to do an air boat ride in a swamp - we just turned up and had to wait about an hour. Five years ago, we took or son to the same place and were turned away - we arrived mid morning, but that day was fully booked. Just shows how things have changed.
The internet changed it as venues discovered they could set up pre-booking systems cheaply which gave them guaranteed income and the ability to spread visitors numbers more evenly. They'd deliberate restrict the number of tickets for sale for peak times to "persuade" visitors to buy tickets for less popular days and start/end of day times.
Of course, lots of places still have ticket sales available for the day itself, but it's getting fewer and fewer, especially the busiest places who know they can sell all their tickets in advance. Why wouldn't they? The less popular places still need the ability to sell on the day - why would they turn people away if they aren't full?