Oh look, Google's 67th messaging app attempt. I'm sure it's going to be a killer this time...
Preset responses, seriously??? bwahahahaha, only a socially challenged googler could've thought of something like this.
I'm guessing that they've got some pretty good experience with the reception the same feature has had on Inbox, where its been around for a while. Just because its not something that seems useful to you (I rarely use it, but it has sometimes been useful for quick and contextually appropriate acknowledgements) doesn't mean it doesn't have value to the broad base of users Google is targeting.
The responses aren't preset, they learn how you respond to certain scenarios. Not everyone is going to have the same choices, it just makes your generic response easier to send.
FYI, they use ANN to understand your messages and only then show choices of quick replies. Think of it as a simplified google search auto complete, which at least personally saves me a ton of time.
I'm guessing that they've got some pretty good experience with the reception the same feature has had on Inbox, where its been around for a while. Just because its not something that seems useful to you (I rarely use it, but it has sometimes been useful for quick and contextually appropriate acknowledgements) doesn't mean it doesn't have value to the broad base of users Google is targeting.