Super Mario Maker on Wii U was a pretty big success, especially in the YouTube Let's Play realm. Given that Wii U had significantly fewer sales than the 3DS, one would think that a 3DS port of Super Mario Maker would be even more successful and a no-brainer. Well, that should be the case, but sadly it's not.
Super Mario Maker 3DS, due out on December 2, 2016, will launch without online level sharing. It will launch with 100 Nintendo-made levels and a rotating list of 100 levels made by owners of the Wii U title, which still gives players potentially never-ending content, but all of these features are consumption and not creation, which is a major draw to the original title.
Now, it's entirely possible that players who just want to play levels will still be interested in the title. But many players of the Wii U title dipped their feet in a few custom made levels before trying their own hand at creation. 3DS players have a significant handicap on that front. They can only share their creations via local wireless and street pass. Meaning someone could make the best Super Mario Maker 3DS level ever created, and the only people who will get to witness it have to be lucky enough to pass him/her on the street.
At that point, anyone who plans to do more than just dabble in creation wouldn't even bother on the 3DS title, and asking those who would buy the same game but tethered to a wall outlet is too much. It's unknown whether it's a system limitation, or if Nintendo doesn't want to ask too much of the 3DS user base, but given how successful Super Mario Maker was on a significantly less successful console, a fully functional 3DS version would have breathed a whole new life into the title, especially with cross play features that already exist between the two. Perhaps a Nintendo Switch port is also in the works with its portability?