Here's the problems with what you have proposed:
BC: Had plenty of progression in dungeons, just like its predecessor, Vanilla. Raiding was a lot less accessible than Wrath+, so many people mostly did T4 and Dungeons/Heroics (I personally was one of these players, and now I'm bored with HEROIC raiding). There was no LFR/Flex for people to do, so dungeons were really important at the time.
WoD: Has a ridiculous amount of raiding accessibility and progression via LFR and "Normal" (Flex). You can almost jump right into LFR (or even Normal) when you hit 100, and if not, run a dungeon or two to boost your iLevel up enough, then never return to the harder-than-LFR-stuff-that-gives-less-iLevel-loot.
While I do agree that they're getting a bit too comfortable giving us less content (WoD especially, having no new class, race, nor new 'system' outside of the stat squish and the two new stats), Dungeons aren't really going to be too prevalent in the upcoming expansion(s) because of LFR.
That makes me so sad. Dungeons are my favorite type of content.