It really is deeper than Android just not doing it. Android does do it -- hence how it works for T-Mobile. The carriers are making it where it doesn't work / support native Android. That is the trade off sometimes -- iOS is way more locked down and they control it 100% with no interference from carriers. Android is more open.. It has a base but it can be modified / changed via carriers and stuff. This is also why there are more manufactures for Android phones versus just one.
Most carriers just want you to use their app. If you install their app from the Play Store it most likely will work -- and they do that on purpose because they want their apps to be used versus the "native" stuff. Carrier devices usually come with them pre-installed.