re:
Why? Because they still get people buying their hype. (And they do have pretty good coverage.) TMobile lowered its rates because even though they had decent coverage (where I am, they have about the best coverage), they didn't have as many customers as they wanted to. Sprint? They've never had good coverage (which is why they bought Nextel, figuring that they would get both the huge customer base and the good coverage - both of which ended during the band changes), and they have mostly independently owned stores, with "associates" who are no more than sales people trying to upsell as much as possible, but unable to handle even the simple problems we handle here (and, as far as I know, no one here works for any carrier).
In Florida, the place most people east of the Mississippi retire to, a 55+ plan makes sense for any company, cellphone or not. But in Virginia? Not so much.
But if T-Mobile gives you the coverage you need, go with them. Or, if you don't use much mobile data, go with Mint. 2GB/month is only $15, if you pay for it annually. (And it's on T-Mobile towers, so you get the same coverage.)