Note: this isn't really in defense of Nintendo, so much as of ports in general, and it goes a way towards explaining why we've seen a pretty significant uptick in the number of rereleased games from almost every platform holder and publisher this generation.
Some uninformed gamers (that's not an insult, nor is it aimed at you, OP) see all the ports, remakes, and remasters this gen and assume that these recycled games are taking the place of new projects. However, ports cost a fraction of the time and manpower that new games do. So, while it can be wearing to see the same games trotted out over and over again, the truth is that rereleases don't (usually) divert resources from the development of new games. Many are contracted out to outside developers, or have the heavy lifting done by support studios and secondary teams. Those that are dealt with in-house are almost invariably worked on concurrently with other projects. Since companies have a finite amount of time, money, and manpower, they can only put out so many new titles in a year. Thus, the choice for publishers isn't "put out tons of ports or tons of new games," but "put out a handful of new games and nothing else, or throw in a few ports to pad out the release schedule." Knowing this, I don't really mind remakes/remasters/ports from any company. Far from reducing the number of new games I can play, the cash flow from rereleased games goes back into the company, (presumably) funding the development of new games, which will one day also be rereleased.
As for Nintendo specifically, their bringing ports to the 3DS extends the platform's life, serves the existing fanbase, and pulls in money from that huge install base, all without taking too many resources away from Switch development. Ports to the Switch help pad out the roster for the first half of the console's second year (the usual time for a post-release drought and "no games" complaints on any new platform), while also giving titles that failed to live up to their sales potential on Wii U a second shot. The Switch itself is also an especially attractive platform for quick third party ports because of its early success, and the added bonus of "play anywhere" novelty it gives old games (see: "Dark Souls on the can" lol). Its conventional internals also make it a simple/cheap platform to port to, maximizing potential returns. The only reason it isn't seeing more third party sup-port, IMO, is its limited power coupled with just how unexpected its success was as a followup to the Wii U.
That, as I understand it, is why we're seeing so many ports on Switch, and why it's not really a bad thing. I think the real question here is, as you said, "Where are the new big games for 2018?" That is where Nintendo is falling down a bit at the moment, and hopefully something they'll have a good answer for come E3.
