I think the biggest improvement is the ability to understand the context of a sentence instead of just listening for keywords. I'm not saying it's a conspiracy

I think the biggest improvement is the ability to understand the context of a sentence instead of just listening for keywords. I'm not saying it's a conspiracy because there's just so much data and lot of it probably isn't even useful. However, the recordings are definitely used to improve the ability to recognize the way different people say the same word for the purpose of improving recognition in the future.