I don't see why you would need high IQ either.

Not necessarily high, but higher.

Basically, each job has an appropriate IQ range. It's better to pick people from the higher end of that range than from the lower end.

Work habits, etc, can be judged by someone's ability to get things done, which can be judged from their resume as per standard recruitment procedures.

No, I don't think you can effectively evaluate things like work habits on the basis of a "normal" resume. There is a reason people are hired after interviews and, sometimes, test periods and not just on the basis of their resumes.

You seem to think IQ is a better indicator. Why?

IQ is not a better indicator of work habits. However it is a good indicator of the contribution that a person can make to your organization. To make obvious observations, people with higher IQ work faster, make fewer mistakes, need less things explained to them, can handle the unexpected better, etc. etc.

Work habits, etc, can be judged by someone's ability to get things done,

These haven't been as extensively studied, but anecdotal evidence suggests these are also correlated with race. Furthermore, since judging these things is obviously going to be more subjective than looking at the results of a test, an employer relying on these is going to be even more open to accusations of racism.