I have a few thoughts. 1. To save on production costs, Microsoft decided to go with polycarbonate. Lets be honest, putting a 2k display on the phone, new USB C, and an actual retina scanner isn't going to be cheap. At least not cheap enough to make a good enough profit margin.
2. Microsoft is being more secretive than we think. These two phones look like the Lumia 640 and 640 XL, budget phones. What if the Surface phone is the actual flagship? Come on, Microsoft knows how to makes good looking devices, Surface Pro 3 -- Lumia 930... why would their first real try at a Microsoft Phone look just okay. Besides, Lumia as a brand is all over the place. Their are great phones and really cheap phones. Not the best brand for Microsoft to use to reinvent themselves with Windows 10. The Surface Brand is a much better platform to launch for a phone. Microsoft is really pushing the Surface Brand with Pro 3 devices in the NFL, on shows like Arrow, The Flash, Marvel's Agents of Shield, and Tom Cruise had them throughout Mission Impossible 5. I go into more detail at cjdrumm [dot] wordpress [dot] com. Let me know if you think or if I am way way way off.