Why? The SP4 does replace a laptop, but there's still a trade off there. It depends just how productive you want to be on the go.
The type cover is amazing for its size and weight. But it is still a thin and relatively small keyboard. The Surface Book has a more robust keyboard but is thicker and weighs more.
I feel like the SP4 is a laptop replacement. But the Surface Book can be also while also acting like a laptop in some situations. They're both interesting, just boils down to the user's needs.
I'd likely buy a SP4, but can understand why others would be a SB.
The type cover is amazing for its size and weight. But it is still a thin and relatively small keyboard. The Surface Book has a more robust keyboard but is thicker and weighs more.
I feel like the SP4 is a laptop replacement. But the Surface Book can be also while also acting like a laptop in some situations. They're both interesting, just boils down to the user's needs.
I'd likely buy a SP4, but can understand why others would be a SB.