So they could sell you DLC in the form of the Tingle Tights probably.
Tingle also kinda got run out of the map business with the Sheikah towers working the way they do, but I could've seen them implementing him into BotW as a way to point you in the right direction to find discoverable landmarks that go toward your map percentage, perhaps. Maybe with him telling you how many in the current region you're in are still left to discover or something like that. Or maybe even for a very very modest price of 398 rupees he would let you copy down a landmark from a region off his map!