You're right; it's not plagiarism as that would be relevant in an academic setting and serves as a warning against behaviour which (outside the academic setting) is much worse.

What you're doing is closer to theft; but largely - copyright infringement. You're positioning yourself as an appropriate person to financially benefit from the work of others by ostensibly presenting the work of another person as your own. It weakens the platform and exposes the administration to potential take down requests. By doing so; you're acting as a greedy bad actor.

You might not care yet; but international copyright law might make you care. :)

Please stop stealing other peoples work.