Why are there sequence point guarantees for C library functions?

Question

I am looking at the C23 draft standard, but I think this would apply in C11 as well. There are several guarantees about sequence points in relation to function calls in C, such as before the return of any library function and between sorting and search algorithm calls to comparison functions. I feel like I am missing something, as my understanding says we don't need these guarantees because we have 6.5.2.2.8:

"There is a sequence point after the evaluations of the function designator and the actual arguments but before the actual call. Every evaluation in the calling function (including other function calls) that is not otherwise specifically sequenced before or after the execution of the body of the called function is indeterminately sequenced with respect to the execution of the called function."

This implies as I understand it a sequence point (or the same effect) before the return of any library function and between any comparison function calls. So we don't need those specific guarantees.

Is this a (somewhat confusing) redundancy, or am I missing something?

EDIT: The comments below give two good reasons for the guarantee for library function returns: a library function may be a macro or may be written in assembly. However, the question still stands in relation to the guarantee that comparison function calls are sequence point separated from eachother (and from element movements in the case of sorting). This is only one redundant assurance at this point, so maybe it is just redundant and there is nothing more to it.