If we're fair, you not knowing why recruiters often but not always suck, is in a sense a status signal itself. Recruiters suck because most of the time, they literally don't do anything useful, nor do they even usually have direct contact with a hiring manager. Quite literally, most of them just accept a CV, then give you the HackerRank test you'd get anyway, if they actually work for the company. If they don't, you get to pass every line of communication through them, maybe even letting them modify your resume so it obscures your own contact details, before you get that automated test.

That said, some are fine.