The reason is simple. I had set it to free and I was getting many A2A requests, about 10-12 a day. The problem was not the number of A2A requests, but it was the number of personally offensive questions that were asked about me and then the stupid question asker would have the audacity of A2A me (Anonymously, of course). Now, they might still be asking those questions, but I don't get to see them and I am very happy about that. Last couple of weeks were just brutal. So, I had no choice but to raise my A2A price. I really don't care about the Quora credits, but don't want Quora to "boil my blood" either almost every day.
I would still prefer it to be free. But, I just don't want to be overloaded with questions that personally attack me. (I am sorry, but I am not that tolerant. Still learning that wonderful quality. My students and Quora are accelerating the process of learning tolerance, though.) If Quora can come up with a solution or if someone else has a solution, I would be happy to hear it.