Regarding the two Russian A50 shot down during the Ukraine war, but it would also apply to US style AWACS.
Beside the price-tag of the plane itself, I would expect that the crews operating the radar are also highly trained, and that if it may be even harder to train a crew than to build a new plane.
I know, that something as simple as pulling the big-red handle on your paraglider harness is pretty hard when you’re in a severe flight incident dealing with G forces and the ground moving full speed toward you, and I imagine it’ll be even harder on a large plane, where you need to access a escape hatch, most likely in a burning and depressurized cabin while having no idea where is up/down due to the G-force and the rotation. However, when flying a plane which like a high value target for the opposing army it would at least feel more comfortable to know that you have a low but non zero chance to escape if you’re shot down.
I don’t think the design of the plane allows for it.
In fighters, it blows the canopy, triggers a rocket in the seat that gets the pilot clear of the disintegrating plane, and eventually deploys the chute.
These types of planes don’t have a canopy. They’re also much larger, which means it’s much more difficult to get clear.
You don’t necessarily have to have ejector seats - WW2 era bombers for example relied on the crew making their way to a hatch to bail out. Despite being a considerably lower chance of survival than modern systems (not helped by various positions having to crawl through narrow spaces to escape and/or find and put on their parachutes due to not having space to wear them during normal operation) the option of bailing out saved a large amount of people.
Most WWII planes were brought down with gunfire, or other passive projectiles. These tended to do small amounts of damage, that added up. E.g. A plane with 2 damaged engines on 1 side, and a cut fuel line on the other, can still glide for quite a while.
Modern missiles are designed to do maximum damage over a large area. A missile hit will generally render an aircraft unflyable. The aircraft will be in an extreme tumble, if not coming apart completely.
In short, a modern plane being shot down won’t give the crew a few minutes and a stable platform to bail out from. It will be a tumbling whirl of wreckage, rapidly approaching the ground.