Why do people make it like a contract temp job is different from permanent one even if the role is the same?

If you are applying for developer and one position is 6months while another is no duration why do people like to ask questions like why not apply for full-time? They make it like I should only apply for full-time like role so the moment contract period is mentioned I may as well strike out that option and nearly half of full-time job are contract too. So I am not really understanding at all.

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