I completely agree with you, they shouldn't shut the dungeons... But just want you to notice one thing.
While it seems that DRC will be close both in HM and HM7, for GLS and AA it seems wll be closed only HM7 (since you mentioned GLH).
- Dark Reach Citadel (Hard / Hard, 7 players)
As you can see, they way they wrote it seems to imply this.
- Grotto of Lost Souls (Hard, 7 players)
- Antaroth’s Abyss (Hard, 7 players)