I wonder if publishers are just delaying or waiting to release their games on Switch because they want to sell more of the game. If you buy the Switch version you get a console and a handheld version, so you wouldn't need to buy another version. But if they delay the Switch version, then people would buy the PS4/XB1 version and then have to buy the Switch version later to get a handheld version. It just happen so often that it seems like a strategy at this point.
That wouldnt make too much sense, also that wasn't case with Crash, Crash for Switch was released alongside XB1 and PC versions of games, Switch version of Spyro can easily be released alongside PS4 and XB1 versions of games, it wouldnt be strange if Nintendo keep back announcement for Nintendo Direct.