Windows Phone doesn't run on a fraction of SoCs that Android does. You are basically limited to a Snapdragon and that's it. There is no such rich ecosystem like in Android, ranging from MediaTek to Nvidia.
It's like criticizing Windows, that it doesn't run on Chromebooks or PPC Macs.
The issue is whether it will result in better product, where better is defined as "will it sell more?". Your average cellphone buyer does not care about that. But he cares about thinness and battery life, which would be affected by a more universal platform.
Imagine a 3D chart, where one axis is battery life and small-sized hardware, second is versatility, third showing the sales, with a curve going through, showing a compromise between two trade-offs and total sales for that compromise. We are currently in one point, with few people arguing to change the position to another point, completely ignoring these two other axes.