In my mind, the full stop “sounds” like dropping the voice at the end, like you do at the end of a sentence.
And in speech, dropping the voice at the end of “Great” would sound sarcastic.

Whereas an exclamation mark “sounds” high-pitched and excited.

And no punctuation is so normal in text that my mind “adds” the expected sign at the end, which after “Great” would be an exclamation mark.

It’s really hard to explain, I hope I’m making sense.