cuz it takes time to make games. Third parties weren't sure how the Switch would do after the Wii U failure, so most of them probably had nothing in the works for the Switch when it launched. Despite this the Switch managed to get some older ports of popular games already. It would probably take a lot of effort for games that were built to push ps4/xbone to be ported to the switch, so instead we're getting older ports. I'm sure a lot of games got started for Switch in 2017, by late 2018 and in 2019 there will probably be strong third party support for the Switch, including new AAA games built for it, not just crappy C-team ports of games like Nintendo owners have gotten used to since the Wii. So far its pretty much indie games plus Nintendo's big hitters that have driven the Switch. But within a year AAA third party support should start hitting and helping to drive Switch success.