is a minecraft thing, if you want to low the spawnrate of this structures you have to use datapacks
tha one is just a coincidence, like exposed mineshafts in a big cave

The open air behavior for both of these dungeons is intended because they were first designed for 1.16, when caves were much less massive. I may consider fixing up this behavior to be more compatible with massive caves in the future, but it's a low priority item. Thanks for reporting though!