One of the reasons. In general, I can see a low rate of acceptance of .NET among the crowd which has a high rate of interest in Clojure. I guess it is a case of avoiding Microsoft-dominated technologies by the open-source crowd.

As someone who uses both, I'll gladly be a supporting data point for this hypothesis.

And the Microsoft crowd is sometimes reluctant to embrace non-Microsoft technologies.

This is true, but I think the reasons are different. There has been a lot of usage knowledge created around the Microsoft platform(s), some supported by the community, but a lot still supported by the company. Moving in the open-source realm means losing a company's support, and I can see how those who are not used to it are uncomfortable with it.

I don't see how that's too different than if a dedicated open source user was to move to using MS products. Replace 'Microsoft' with OSS and 'company' with 'community', and the statement is still true.