ehrm are you aware of the third party lineup for the PS4 and Xone for the first year they were out? beyond the initial launch month they were a bit empty too, at least as far as anything particularly exciting. third parties rarely fully jump over immediately, particularly with Nintendo's case. If we're to say 6 months ago some big third party studios decided they'd want to put some larger titles on the Switch, they still might not come out for a while. Depending on the size of the game conversion can take a while (at least if you're going to downgrade visuals or make some tradeoffs to allow the game to work portably).
That and the fact that Nintendo seems to be pushing for relatively short announcements/release dates (i.e. Doom last year). So for all we know there are some big third party games coming this year that are waiting to be announced. In the end it's Nintendo's call on when these things get announced. I expect some big third party mentionings in the Direct that will likely occur in the next month (they're not going to have a mini direct only for the first portion of the year and leave question marks in everyone's minds).