They probably also likely removed it, because if you open your browser's debug window, it identifies clearly that T-Mobile is the backing carrier, not "the big three carriers" like they claim. It's T-Mobile's classic MVNO coverage map, if one is familiar with it (which will include possible roaming on other carriers, so they're not "lying"...)

That coverage site is also running on a very old system, IIRC, so good luck finding an engineer that still works there and knows how to fix it to "update" the gulf.

(Cell nerd deets, Mango-Mobile is using Liberty Wireless as their backing MVNO, which is an MVNO on T-Mobile's infra. Liberty was also already terrible. MVNO's are virtual cell carriers that live on real ones. It is NOT using Verizon, AT&T, or even Dish, except possibly in the case of roaming agreements.)

T-Mobile also use Muskrat's Starlink as their mediocre sat-to-cell service, and they also leveraged Mango's position in his first term to push through M&A's to acquire 5G spectrum to artificially accelerate/cheat past the others. John Legere fans, cover your ears, he actually went to Mango's FCC quite a bit to get this going.

tl;dr: probably a good idea to add T-Mobile to the boycott list next time one's looking for cell service. (As well, any T-Mobile MVNO like Mint, MetroPCS, etc. Here's an MVNO List that can be sorted by host network.)