AB+ are all "blood is blood", but nobody wants their shit-tier dodgy blood!

Yeah we don’t really mix blood types at all here in Lebanon, and I really doubt they do anywhere else. Universal donor and universal recipient is just theory, in practice it’s easier to receive O- than AB+ because AB is really uncommon (as is the case everywhere).

AFAIK the A/B and Rhesus antigens are not the only markers and there are more blood compatibility components that are taken into account if possible.

I have a relative who has an unfortunate condition that causes internal bleeding. They've had enough blood transfusions that their antibodies are completely haywire.

Multiple times, doctors have not listened to their protests, and given them O-. They turn an impressive shade of yellow (among other, more serious, issues).

Last I heard, there were 2 compatible donors known, 1 in a different country. Thankfully, you can store blood longer term. It's just not cost efficient to do in bulk. They have their own little stockpile of blood at their local hospital (mostly self donated).

D-:

I presume they would do as many O- people do and have blood drawn for their own use if they expect they might need it

It's expensive and blood can only be stored for so long. Easiest to stick with compatible blood types.

There are also loads of other antigens in blood that can cause a reaction. These are just the commonly known ones. So blood should still be cross matched anyway if it isn't an emergency.