Moving on from the Hero of Ferelden

I think it's because the Hero was the first protagonist of the franchise. Also, many fans think that DAO was the best game in the series, and the Warden was the main character of that game.

Many reasons, I think, that sometimes differ from person to person. One reason would be attachment: there are many who are attached to their Warden and so would like to see them again in some way or another.

Personally, I love my Wardens but I would not want to see them again because for that to happen, it'll be more than likely mean that all of the living Wardens' endings would have to convene into the same story regardless of the individual Warden's characterization. It wouldn't make sense for my canon Warden to become involved with, say, the Grey Wardens again. I could deal with the search for the cure but I don't want to deal with anymore of this. That's why I'd rather the Warden's post-Origin existence be left for the individual player's mind.

It's the same with my Hawkes. 

Dead hero, Orlesian Warden-Commander killed the Architect and Mother, Bodahn, Dagna and Leliana are sad. Wouldn't trade it for the world.

Bring back Hawke, though. I love that guy/girl!

Once they were brought Hawke back. Or some disappointed bitter imposter, who whined about blood magic and some responsibility, not my crazy-happy freedom fighter. Probably he ate my Hawke... poor guy. (True, he had some good moments too.)

The Warden's voicelessness allows people to project more of themselves on the character, and thus creates a greater attachment.

Also Bioware haven't really been great at leaving the Warden in a place that feels like an ending. I mean, DA:O itself was actually OK as an ending for most wardens (Morrimancers had unfinished business, but otherwise things were pretty resolved), but then DA:A's epilogues made things more up in the air, then DA2 dropped the "disappeared" bomb, then DAI had them on an important and unresolved quest. Trespasser does effectively give an ending to Lelimancers, but not really for others.

edit:  They should really stick in a codex entry in the next game that boils down to "The Hero of Fereldan and [Love Interest] lived happily ever after.  The End."  Though admittedly that gets more complicated if they still want to do stuff with the LI, which they probably do with Morrigan at least.

DAO was originally supposed to get two years of support and DLC, so we may have gotten more DLC as a result that may have explained the disappearance.  But that got scrapped in favor of DA2.

I say if we want the further adventures of the Warden explored, we should use our own imaginations.  Then if our HoF gets "ruined" we have no one but ourselves to blame.

I, for one, am perfectly content with the HoF never coming back. Mike Laidlaw also expanded on the reasons behind the decision recently:

It is perfectly understandable, I for one would have very high expectations if they ever did bring HoF back. Clancy Brown being the voice actor would be the first one. It is impossible to do justice to the Warden

Warden arrives dressed like a chantry sister because he still has to lie low and sneak past borders after the last time someone asked him to help with something important. 

I think the reason why people want the HoF to return is because Bioware keeps stringing those people along and then turns around and says, "They are not returning."

If the Hero's story is in fact done, then why the hell is he/she on some random mission to cure the Blight. Their story does not sound done to me.

I really do not care about the Hero not making a reappearance. But Bioware needs to get it together and understand what the word, "Done" means.

For me, they never ended their story. Sure, you can choose to kill your Warden (I may just do that in future playthroughs) off, but I'm not going to waste hrs upon hrs of gameplay if (that's the key word here) there is a way to keep them alive. It's the how they choose to end DAO thats part of it too. The king or queen ending: how is that not tearing Ferelden apart? "Missing" their King or Queen? Also, there a possible love interest to possible Divine? It's not like HOF rode off into the sunset or anything like that.

I use to point and laugh at all the people who couldn't get over the Warden not returning. Then DAI came out and all I keep hoping for is that I can play my Inquisitor in the next game...now people laugh at me. True story.