Contract termination usually means that parties settle their obligations in a way that terminates the relationship fully. The plaintiffs may not have expected this, but consider the patently unjust situation when customers can cancel the contract, while T-Mobile still must provide financing for their handsets (which is what the plaintiffs want). Why would it be in the public interest to force T-Mobile to do that?

This is a case of somebody not thinking things through, and not reading what they're signing. T-Mobile may be more explicit, but should they be forced to explain every possible contingency? That's why the print is small — because reality is messy, and there are so very many corner cases.