How come after the spell is broken everyone is still called by their Storybrooke names?

Well, David's name actually is David in FTL. Charming was just a nickname.

Emma is the only one whom I've heard call Snow Mary-Margaret. And, since she's only ever known her as 'Mary-Margaret' that makes sense. Henry might too, but he's in the same boat as Emma.

We haven't really seen Ruby since she got her memories back, and I don't remember what they called her In The Name of Brother. Snow called her Red the last time we saw her.

People bounce back and forth between Mr. Gold and Rumpelstiltskin, and there really doesn't seem to be a rhyme or reason to it.

You also have to remember that the characters aren't all from the same world. We've got Frankenstein's land, Wonderland (and who knows how many more) characters all in Storybrooke whom have never interacted with each other out side Storybrooke. They only know the people in the town as their Storybrooke counterparts.

That Is A Good Question, But What I Believe Is That, Being In A Curse For 28 Years, I Think The Name Will Stick With You & Will All That Time I Think They Wouldnt Even Notice, Even Thou Ruby Is Actually Red.

I think all the characters are more consistently called by their cursed names. Remember that party they had when Snow and Emma came back from FTL (probably the first time everyone was in one place since getting their memories back), there was a huge banner that said WECOME BACK MARY MARGARET. its kind of silly if you ask me considering how many less letters would have been needed to write SNOW.

As to why they seem to prefer their cursed names I'm not really sure. Maybe it feels more natural in the real world setting. Maybe they made an agreement to continue using their real world names just in case some stranger shows up. I personally prefer their FTL names and hope they switch over now that they are leaving Storybrook.

actually Charming's name in FTL was James, not David