Possibly because the surface 3 is ultra portable, the surface book is anything but? I dint know, maybe email Microsoft.
And I dint know what you've done to your device to be talk I g about logging in and trouble shooting. I hit the hotapit button. It works. Every time. Flawlessly. This is 2016, why would I need an additional contract for something my phone does perfectly for free?
The very short answer is that there probably won't be an lte option, because there isn't a market that justifies it. Deal with it. Why can't MS offer every coy with every ram and sad combo? Because they have done a market analysis and it most likely makes no financial sense to have so many SKUs. Microsoft are not Apple, they have learnt the hard way to be cautious with their stock levels.
You could just buy a dongle if it is that important. Question. How many laptops do Apple make that have SIM slots? Why is that?