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.