The success isn't a surprise to me. This is my opportunity to get an "I told you so" in. Back when the Switch was announced, I predicted it's success, and most of the reasoning and logic I used is now commonly referenced with the benefit of hindsight. I saw this coming, and provided credible arguments to support my predictions.The success is a surprise to everyone.
Plenty of other people didn't see it coming, including quite a few major game publishers. And yes, that is why we are seeing so many ports and quick turnaround projects coming to the Switch. Making a game from scratch for a new platform is time consuming and costly. Porting content you produced years ago is economical and a chance to re-monetize old material.