Doesn't surprise me much. The switch, in terms of how it is played, is closer to the 360/ps3/X1/PS4 than the 3ds was.
So, any game that isn't too demanding can be immediately ported over.
With the 3DS, games had to better fit its more unique control scheme (for the longest time, it only had one stick) and have a way to make use of the second screen.
Fewer games made sense to be ported to 3DS.
Those things and Switch's popularity out the gate make devs hungry for new markets and ready to quickly port their existing games to switch.