I don't know why exactly this is happening but i do know if they really wanted to stop this they could ban Bitcoin now and close all related bank accounts. But they won't because someone has an agenda here and is probably making a lot of money.
Read this article
http://bitcoinblog.de/2014/04/28/chinese-banks-dont-know-how-to-act-appropriate-cause-bitcoin-is-too-tiny/TL;DR Banks don't care about Bitcoin. They don't really give a sh** about closing the accounts. They find weird that PBOC is pressuring them over such a small issue. PBOC is having trouble closing the accounts and even had to send two of the second highest rank officials to interview the banks
You've probably already read it anyway. I agree, someone is making a lot of money behind the scenes