Why do some companies recruit online every day? How to correctly distinguish which companies really need to recruit people and which are selling advertisements?

Generally speaking, companies post recruitment positions on recruitment websites, but because some companies have long-term contracts with recruitment websites, the positions will last until the end of the contracts, and the websites will automatically update these recruitment positions every day, so sometimes companies have recruited enough people, but there are still some vacancies. When candidates see them for the first time, they will think that they have just been released.