Because it has a high likelyhood of being written completely by a LLM without any human thought or attention being put into it.

Being written by a LLM is a signal that the submission is of low effort and therefore probably low quality, which then puts the onus on the people reviewing and reading the submission instead of the original generator of the submission. Hence I would classify it as spam.

Open source communities also have rules against LLM generated contributions, for various moral, ethical, or legal reasons.