Colleges may give generic credit for an IB diploma, but that is not necessarily the same as getting useful subject credit. The content of IB courses may not necessarily match up to that of frosh-level college courses at US universities, so a student with credit for an IB diploma may find that such credit is not especially useful.
AP scores and college courses taken while in high school may have similar issues, but at least they are more likely to resemble other college courses in US universities (unlike IB, AP is mainly a US thing, while many common frosh level courses are similar at various US universities).