Don't know if you're actually asking why this happens, but it's because their executive functioning skills are immature. It's an annoying overlap because when they're younger you expect to need to cajole them a bit more and you're hoping they will be a bit more mature and self-starting but they won't catch up here probably until they are adults. Part of that is developmental and part of it is just the lack of perspective that these things don't just magically get done for them but are the result of a real person's labour.
I would probably start moving away from consequences like lost screen time, as they're less useful once you're moving into teenhood anyway. Unless it's stuff like "wifi gets unlocked once you've done X, Y, Z task." as that kind of thing tends to work better - this privilege is conditional on that responsibility.
The approach in the book Raising Human Beings by Ross Greene is also great for preteens IME.
For washing - 12yo could probably do their own especially if you have a tumble dryer, in which case leave them to it. Otherwise, or if you are using the washing machine too much yourself to allow for an open schedule, I'd probably try tacking on a reminder "Don't forget to check the floor". If they need uniform midweek could they stick a wash on themselves - if they do have to hang it up then that's annoying for them, which is likely to magically help them remember when you offer to do it for them 
(This is basically my rule for my 13yo - I do his washing as and when, as long as it's in the laundry bin. If he wants more washing done at another time then he can do it himself.)
If you want to go out would it help to have a general rule that everyone needs to be dressed by X time at weekends, so that you're never waiting around for people to get dressed at the last minute. It probably means more huffing at children to get dressed, but at least it wouldn't be holding anything up.
Shower by X time otherwise earlier to bed the next night as they "clearly need more time to get ready".
Set table - sorry don't know on this one. We are awful and all eat in separate rooms in front of screens 🙈
Dishes - DH docks screen time for this, a set time of day where all dishes are collected for dishwasher works well. If you check later and find more, perhaps the dish-hoarding child could wash those dishes by hand? Like the laundry one, this builds appreciation for the fact that having to bring dishes to the magical washing up machine is really no big hardship at all.