The reason that there are still pending tasks for your consumers, even though you removed this requirement from a future minor version, is because your consumers haven't acknowledged the major version of the document that they were first assigned.
By design, the system does not require re-acknowledgment on minor updates in Documents since minor updates are considered to be small edits that don't change the general nature of the document. You'll notice that because your consumers haven't taken action on the major version of the document from the previously required acknowledgment, the system is updating the pending action with the most recent minor version of the document for the consumer to acknowledge. This is because this is their first acknowledgment on that document's most recently published major version. After the first acknowledgment has happened on the current major version of the document, future minor updates before a major version of that document is published will not require additional acknowledgments, regardless if making acknowledgments required.
If you want to remove document acknowledgments from consumers, you will need to publish a major version. However, this will affect being able to add this requirement until the next major publishing of the document.