I wonder if its a issue of WDW not wanting to pay to staff more people todo crowd control.
Nature of the beast... that is, humanity. No one want more work or more complicated work. If it were up to Ops, I'm sure they'd be happy with a 'dead' park every day.
On top of that, when attendance was mostly unrestricted, crowd control becomes unbearable and nearly unworkable. When the hub is absolutely packed with people for the fireworks, Ops has to keep walkways open for safety, otherwise someone with a medical emergency (or a fist fight breaks out) can't get the attention they need from first responders.
I've been trapped in the "you can't stand here so keep moving" walkways unable to get into the crowd at the hub and being constantly pushed along until I either find myself exiting the park or in front of Speedway.
Ops don't want to deal with that. Especially when fireworks and a parade or a castle show are back to back. It's just untenable.
That is why reservations and dated day-tickets are sticking around. To keep those types of crowds happening.
When people think back to the days when they were able to have fireworks and a night parade, they're remembering when there were literally 10 thousand less people in the park at that time.
Now, this is when people complain that Disney didn't increase capacity as they should have. And this is where I point out that extra *ride capacity* doesn't do anything for extra *hub capacity* for the fireworks and parades. In fact, building more rides in MK is going to bite them on the backside because the infrastructure is already maxed out.... unless they hold the line with reservations and dated day-tickets, which will only beget more customer moaning at being locked out of the park on the days they want to go.