I want to clarify a few things:
1. ANet never really had a dungeon team post launch, any time a dungeon needed to be created (F&F/TA/AC redo), people who wanted to work on that project got together and then disbanded after.
2. Robert Hrouda was fired because he didn't like the idea of his work being used as temporary content.
3. Dungeons, outside of redesigned AC, TA (aether), and Flame & Frost are all devoid of mechanics and have HP sponge enemies. There's really nothing interesting to be said about alot of it. It's obvious as ANet designed small group content post-launch that they got progressively better at it.
4. Fractals were concepted, prototyped, and released in 8 weeks. It's clear that by comparison, it is a lot less time consuming for them to produce fractals than it is dungeons and you end up with content that is more finely tuned and requires shorter time commitments (typically). Now I know what you're thinking, if it's so easy for them to make fractals, why haven't they released more? The entire studio has focused on the LS since Jan 2013, Fractals got some new releases in Nov 2013 but none since. Now at that time, ANet was still trying to figure out where the game was going as a service, what type of update model to use, how that worked as a company, how to make it work for the player, etc. Season 1 was a lot of experimentation, Season 2 was a lot more concrete in design with the story journal, new maps, etc. Now with HoT approaching, they have finally settled on a direction for the game and they have decided to abandon the Story mode + 3xp paths for dungeons and moved to fractals as their 5 man instanced content going forward.
Fractals are better designed for new content creation, have a better reward system, is better designed for lesser time commitment, has way better encounter designs, and works a lot better for Masteries. Moving the money over to the system that is just flat out better designed and more fun makes the most sense (to me at least).