Quoting:The MS-PL license specifies: "If you distribute any portion of the software, you must retain all copyright, patent, trademark, and attribution notices that are present in the software." Also, source-code licensed under MS-PL can only be licensed under MS-PL.

That's going to throw a spanner in the works of anybody who wants to modify code and then pass it on under a different license, such as the GPL. Also, those who don't believe in patents or copyrights - never mind passing them downstream - won't like MS-PL.