The problem is the development resource limit. The extra dungeons (not to mention a potential new Deep Dungeon) were lost in Shadowbringers so they could put the resources into creating the CEs in Bozja along with CLL, DR and Dalriada.

I suspect they were also getting complaints from some players about them reusing existing dungeon assets instead of creating a completely new dungeon to experience. I've watched that tug-of-war between players in multiple MMOs over the years where one group likes to revisit the original dungeon in a new way while others would rather get a completely new dungeon.

More overall content is always welcome but it's dependent on SE giving the development team more money for more staff so they're able to create more. Or we'd have to wait longer between expansions/patches so what staff they do have would have longer to create the additional content. Considering how many players are already complaining that the patch cycle has been extended from 18 to 20-21 weeks, I don't think the latter would be a popular choice.