We do not have visibility into Facebook's ad approval process, so we cannot give information with 100% certainty why individual ads may have been disapproved.
A common reason for rejection may be that ads conflict with Facebook's ads guidelines. For example, advertising alcohol has restrictions based on country.
When there are issues with the links in the ads, you can use Facebook's Share debugger to check if there are any obvious errors in the links.
If you feel an ad should have been approved but was not, it is advisable to be in touch with Facebook directly. For more instructions, see Facebook's help article on rejected ads.