Why are the details of this deal kept confidential?

The details are secret because they are lying. We can not know the details nor why this deal happened. You should not trust what the company has to say now either because you should not trust people who hide important details from the investing public, customers and their own employees.

These terms are intentional, M$ wishes to deliver the maximum damage with every deal. Secrecy creates mistrust that’s the antithesis of the free software community. In this case they got to threaten another piece of free software dealing with Winblows interops.

To minimize the damage, it is best to assume that M$ did what they did to Novell. They brought an irresistibly large pile of cash to a company that was not doing so well. The worker bees get to work on for another year or two and the executives responsible for the deal get to retire rich. As long as M$ has a few billion to squander, they will be able to do this to small companies. Better terms for this are bribery, conspiracy and fraud.