Because Android isn't very profitable. Android is turning the mobile phone business into a clone of the PC market. When everyone is competing on hardware specs alone, margins get squeezed.
You really don't know what you're talking about do you? Tell HTC that Android isn't profitable...
As for competing on hardware specs alone, that surely explains why HTC developed Sense, Samsung TouchWiz, Sony Mediascape/Timescape, Motorola did MotoBlur.
Nokia could easily differentiate themselves in the same way, combined with their handset design skills and brand recognition I don't see how they couldn't make it work.
Given the choice of that or become yet another Windows 7 handset manufacturer where MS dictate what you can do with the platform I can't see why they wouldn't pick Android.