I think a big factor that people seem to forget is social media. It is way easier to promote your games now and the effect of word of mouth is stronger and faster too. Usually people bought only what they knew, Mario mainly (on Nintendo systems i mean). But i feel like people are now more than ever aware of exclusives, we can only see that with the PS4 compared to exclusives sales on PS3.
Also, having only 1 console, games are most of the time more polish and ambitious, thus far giving better reviews which lands the marketing better and makes the point above stronger. But like everyone said, Switch is a hot item that consumers love, so they like putting money on it.
I would like to add that 1 system instead of 2, i personnally find myself willing to buy/have more time to play games i wouldn't normally play instead of having 2 mario karts, 2 mario 2D games, etc..