I find that often the developers of these apps don't speak English, but want to target an English-speaking audience. For the marketing copy, they're using the LLM more to translate than to paraphrase, but the LLM ends up paraphrasing anyway.

It's insane how most of the dev subreddits are filled with slop like this. I've thought the same thing - why can't they even spend 5 minutes to write their own post about their project?

They are not exclusive to reddit. HN has also been full of vibe submissions of the same nature.