That's their bread and butter. Lots of services depend on people forgetting, or being too lazy, to cancel.
I know for a fact that they have looked into accepting Bitcoin and that these are some of the issues:
1. Bitcoin is small.
2. Bitcoin has a reputation problem(drugs and money laundering, for example).
3. Recurring payments are not easy to implement.
usd has a really bad reputation for being used in shady drug deals, money laundering, etc.