Credit card companies can pretty much do whatever they want without reasonable cause. Most contracts (you know, the three pages of teeny legal print that we don't read) give them full modification rights at any time for any reason. Negative creditor activities generated only by negative debtor activities essentially were just self-imposed rules they followed out of courtesy.
I had a Capital One card closed on me last month because I haven't used it in a long time. If you're just sitting on credit cards, I highly recommend taking them out every month or two and putting a few charges on them that you pay off immediately.