Not to mention Nintendo sort of lead the way with Wii to 3DS ports, HELL, BN DID do one! That Taiko minigame spin-off they made for Wii's launch got a 3DS port a year or so back, so DOTNW for instance at least would've been ideal, Graces would've also been a great idea.
I'm not sure porting a Taiko game is the same thing as porting a Tales game on 3DS, they already mentionned that porting Abyss on 3DS needed much more work than what they expected originally, every character model had to be redone, battles were only running at 30fps and the game was delayed a few months after its original intended release.
Abyss was also probably the 3D Tales with the less detailled character models, Symphonia DotNW would have been much more of an hurdle and I can't even imagine Graces running on 3DS.
Graces would have been dumb too, it ended up selling much much more on PS3 (it should be around ~450k LTD with the best release currently) a 3DS SKU would have only split the userbase, something they did for years between 2005-2010 and it didn't work at all.
I do agree that Symphonia would have sold more on 3DS... in Japan, but it would have needed a bigger budget to port the game, whereas Symphonia UP/Chronicles was an easy and quick cash grab, are we even sure that the extra sales in Japan from a 3DS version would have compensated the budget needed for development? Not to mention the lost sales for releasing the game on 3DS instead of PS3 for the western audience.
Let's not forget that Bamco also tried to release mothership titles on the most successfull handheld ever and it didn't work, Innocence the first one which was outsourced sold 261k and Hearts which was a full blown mothership title done by the Tales Studio only sold 270k which makes it the 3rd worst performing entry (only ahead of Graces Wii 212k and Vesperia 360 205k).
They also had a successfull port (Eternia 250k) for PSP years ago, the two others ports which followed only ended up selling less than the previous one, respectively Destiny 2 135k & Rebirth 95k, why would that be any different for 3DS ?
It just seems that no matter the platform there's an hardcore fanbase which makes any title sells at least ~100k, but the core fanbase remains on sony home console and it's just easier to publish game there.
I highly agree with Sammy that Vesperia on the 3DS' successor is a very good idea.
At this point, and considering what Bamco is doing with the Tales series, it only does if the architecture of the 4DS makes it easy to port the game.