Mailpile is about encrypted email that NSA may not be able to access. Mailpile also referred to Edward Snowden in their indiegogo campaign. Mailpile also accepts bitcoin payments. Do you need anymore reasons to why this happened ???
It may seem more likely that PayPal froze the account due to discomfort with crowdfunding, but the question then is how many other campaigns have they done this with. Since Indiegogo still uses them, it seems the answer must be "not many."