I have never understood this.
you do have a dalaran hearthstone. Also I agree.
They got annoyed with players developing efficient portal routing for some irrational reason.
Keeps you playing that much longer.
stretches feet in the air and wiggles toes
Maybe they thought that some people might mistake Dalaran (northrend) with Dalaran (broken isles). Still liked that in Legion one portal was to Ancient Dalaran.
Answer your own question:
You already have a HS to new Dal. Why do you want a portal to the same place?
Itâs to make things take longer. The idea now is not âmake the game fun and people will play longerâ. Itâs âmake everything as inconvenient as possible so people have to play longerâ.
probably brought on by the same meanie who came up with Madness/Torment/EotJ affixes
Cooldown.
Also, why Azsuna? Why not Stormheim, or any other zone? Itâs so random.
Because although we were given the ability to âstart anywhereâ to make the game more enjoyable/ open-ended, the actual STORY starts in Azuna and goes clockwise.
Itâs not strictly linear. Since Sylvanasâ ship crashes in Stormheim and that story arc starts there. But the overall story starts in Azsuna and goes clockwise.
I mean, if it were me, I think thereâs validity to âwhich of the 4 zones do you pick?â And the obvious answer is: none of them-- you give a portal to Surmar. Because it has the benefit of being central to all 4 zones, as opposed to dropping you off in Azsuna if you just wanted to go to Stormheim.
Blizz canât really win here. Iâm sure some people like having a BI portal and some want a new Dal portal. But having the portal go to a specific zone that isnât central was⌠a bad idea.
No mages.
Aszuna has mages. 
My guess is that at some point in development, they planned to not have Dalaran at the Broken Shore if the player hasnât completed the Legion intro quests. So, they put the portal nearby. But, then decided Dalaran should always be there, and didnât move the portal.
Idk, WoWâs take 4 portals and get a loading map between each one to get around model is really outdated. Especially when the portals donât take you where you want to go. I want click map to teleport!
Careful this is how we get all âorgimmarâ portals be sent to the Crossroads instead.
Because they thought we would get confused with the portal to Northrend Dalaran. 
this is probably the legit reason (at least lore wise). Azsunaâs ties to the elves im sure made it easier to connect a portal there instead of say⌠Stormheim. The only other viable option wouldâve been Suramar but that was hostile territory at the time.
The one I had the issue with was how for YEARS â for WHOLE EXPANSIONS â we had a portal going to straight to the Vale of Eternal Blossoms⌠until literally JUST BEFORE WE HAD TO GO TO THE VALE EVERY DAMN DAY for the assaults. Just before needing to go there all the time, the portal got changed to Jade Forest. A place no one needs to be for any reason. For absolutely no positive player experience reason at all.

What was the point of decorating the portals then?
You guys look at what the portals tooltip says?
I just looked at what decorations were around them and learned that way 
These are the same devs who thought removing PVP vendors were a good idea because we wouldnât know how to find them. They seem to think of us as some peanut for brains kind of crowd with no intelligence sometimes.
Weâre still here, arenât we? ![]()