I agree that all those are good reasons for a room to be ready late. I'm not questioning this.
But I also thing that when this happens there should be some form of compensation and that it should handled consistently.
Maybe if it's half hour it should be just an hapology, 1-2 hours a drink at the bar or comping the fees for an activity in the community hall. More than that a dinner. Something like that. And it shouldn't happen that the family making a scene at the front desk gets $200 dining credit and the family who says nothing gets nothing.
At WDW I am in Hakuna Matata mode, I try not to let small things ruin my vacation. But we shouldn't let the service fall below a certain level. So we should still politely complaint when a room is ready after 4pm, otherwise in the long term it will become normal to get the rooms ready whenever.
My point is: writing after 4pm is not a free for all. DVCMC contracts with the resorts when the checkin time is. And the contract should be that the vast majority of rooms are ready at 4pm (which I believe it happens) and when it doesn't happen they should try to make it right.
I haven't said that there shouldn't be compensation. And I completely agree that CONSISTENCY in compensation should be important - and ISN'T. And that compensation should be tied to how late your room is ready - getting the text at 4:15 with your room number is different than not getting a room assigned until 7 (and then, walking into that room and discovering its not cleaned or still occupied!). It should also be done in the form of things that aren't going to cost DVCMC or the other members money (or much money), since all operating cost, including compensation, comes out of our pockets. So, yes, a few free extra Fastpasses, drinks or treats (although drinks aren't great because not everyone drinks and some people shouldn't be tempted), or Disney merch (the merch markup is huge - how about DVC waterbottles and bags and coffee cups filled with treats that can be handed out when something like this happens), or flowers the next morning in your room (again, mark up is huge, and Disney has ample nurseries to provide flowers).
What I have said is that its best to have a plan for AFTER 4 - and my original after 4 comment was in response to someone who said checkin is at 4. That After 4 is what we all signed up for. As I said, we've come from the airport at 11 and had a room ready - but I would never recommend anyone plan kid's naps around the room being ready early. That Disney isn't a hotel, its a timeshare, and that creates certain operational complexities. And those operational complexities are going to cause the occasional late check in. It happening once in a while is to be expected - unless we see it happening more and more - and no effort being made to correct it (and right now, with the labor shortage, we may be seeing it more and more for a bit - and correcting a foundational labor shortage impacting a lot more than Disney that has been the result of an event unlike any we have seen in the last century is not going to happen overnight) an incident here or there doesn't mean the service has fallen.
I suspect - because its human nature - that most of the time people arrive with the hope that the room will be ready when they arrive. They can drop their stuff in the room, get a quick shower if they need to, change into swimsuits somewhere comfortable. Its really best when that happens. And when you have kids that could use a nap - its awesome. But honestly, with DVC it seldom does if you are arriving mid-morning or early afternoon. So you start out a little disappointed - not anyone's fault, just you were hoping. And maybe, in planning for the trip, you came here and posted the question and heard from someone who got the text at 9am as they were boarding their plane to Orlando - so your 12:30 expectation seems more than reasonable. I've been there, knowing checkin isn't technically until "after 4" and standing in a line somewhere in Epcot watching my phone at 2 and 3pm for a room assignment that hasn't arrived yet - because until the room assignment occurs, I don't feel settled - even though we are planning on dinner in the park and not seeing the resort until 7pm anyway. But as you do that, the 4pm number gets stuck in your head as a deadline - and when its missed, then what started out as a personal disappointment (it would have been nice to get into the room early) becomes Disney's fault and then people do let the small thing become a big one. Travel days ARE stressful. Getting rid of the 4pm as a deadline in your brain could actually reduce some of that stress.