Here's why:
* "Ac-" is a prefix, but it's part of the root word "acquaint." It's not a separate prefix added to a base word.
* "-ed" is a suffix, but it's added to the verb "acquaint" to form the past participle, not to a separate base word.
Therefore, while "ac-" and "-ed" are present in the word "acquainted," they aren't acting as separate prefixes and suffixes.