At this point the Wii U has just as much of a chance to lead NPD sales as X1.
But in all seriousness, they are probably anticipating Splatoon 2 and decided to wait till July to go all out with Switch stock. June easily to me goes PS4, but July is when things get interesting, because from there on through the holidays the Switch seems to have a big game a month, and if handled correctly I think they can easily surpass 10 million and beyond.