There is one good reason for it: Microsoft
Bill Gates` company supported the dying brand in troubled times, both financially and spritually, when everybody believes Nokia would eventually disappear
There were some attempts to promote Android-based Nokias such as X or N1 models, but despite its extremely affordable costs, customer tend to perceive Nokia as that part of WIndows Phone that should`t be anything else. In fact, Android looks quite strange on Nokia`s format, comparing with Samsung or HTC, so Nokia is likely continue bet on Microsoft, instead of any other partner