It was originally started in 2007 and first deployments started rolling out around 2012. The US carriers were just spectacularly bad at implementing it, so Google swooped in and did it themselves. Then they extended it in non-standard ways and added E2EE. Good, but not standard so also not as helpful as it sounds because if your conversation partners aren't (or weren't, maybe it's better now?) using Google's implementation then your conversations were sent in the clear, just like MMS and SMS before it.