I think the issue is that there probably aren’t even enough people on property to make an after hours ticketed event worth it for Disney and they know it. I am sure they have a thousand calculations regarding percentage of onsite guests who buy ticketed event passes plus local sales and they are looking at their current numbers knowing that it would not even come close to being profitable for them. Honestly I just doubt there are enough people who canceled their entire trip for whatever reason who would suddenly jump back in if given the option to purchase an add on ticket for an event. I don’t know what the costs are in putting on one of those parties but they must have a formula they work off to determine its value to their bottom line and it is just not there right now. Think of the costs associated with providing transportation for those 4-5 hours alone. Then add park staffing, whatever special things they pull together for the event (parade, fireworks, shows, treats), the collateral (wristbands, park maps, signage), the extra laundering costs for the special costumes and the costs that just go into paying staff to plan and execute and market it.
Not to mention I am sure they are not interested in committing to a special event set to take place 6-8 weeks after schools are back in session across the country not knowing what the infection numbers will look like at that time. The last thing they want to do is to create something else they ultimately have to cancel and refund people for. Or something that people won’t commit to buying a ticket for until the last possible moment.