Sprint is a pretty dead brand and provider. They were actually giving away a year of free service without any obligation (you only had to pay $2 tax/fee) and people still would not switch to it.
T-Mobile has pushed the other carriers to bring back unlimited plans and they've separated the phone cost from the plan itself (allowing people to more easily switch carriers and bring their own phone).
Allowing T-Mobile to get more customers and a stronger position might be a good thing in order to compete with Verizon and At&t.