The point of an action item list is to track discrete tasks which have been identified during project execution. Action item tasks may have been previously unknown or unplanned, or they might be too small to warrant a line in the schedule but nonetheless important enough to require team visibility.
Before labeling people as uncommitted, it's important to consider root causes for the action item delays, then address those root causes. So first, consider whether the right kinds of items are being tracked as actions, and whether the team understands why these dates are important. Next,
make sure you as project manager are not unwittingly participating in or reinforcing the behavior! Demonstrating for the team what it looks like to be consistently accountable for commitments is a fundamental responsibility of the leader.
Starting with the latter item first—ask if you are consistently meeting all your dates, whatever actions have been assigned to you. And take a look across all the actions to see what's not being finished on time by you and others. Is it really a lack of commitment, or is there something else going on? (Examining any issues you've had making your own dates could help highlight other kinds of issues.) For example, is everyone just plain overloaded, making it hard to stick to all these dates? Step back and look at the nature of the slips—are you reacting to people seeming uncommitted, but in the grand scheme of things not much has really been impacted? Or are really critical actions slipping that are affecting the project? What about number of actions not being met? The world isn't perfect; some dates are going to be missed just because of what life is like on the ground on a project. Some teams set a threshold and watch——are we making at least 80% of our actions on time? If yes, we're doing pretty well overall. If not, time to look and see what's going on.
What about the actions themselves—are they too granular, to the point of micromanagement, such that the due dates are actually not that meaningful? Or are they truly associated with issues or work such that delays will cause a slip in the project or a big hit to someone's work? As noted above, there should be a good reason for action items to be called out; otherwise, they become just something else to do with people wondering why all those specific dates matter quite so much. No one likes to have additional non-value added tasks assigned and/or someone breathing down their necks on little stuff that doesn't seem to matter that much. We've all got enough to do and enough pressure as it is!
Once you've thought about what the root causes might be, gather the team and discuss quickly the purpose of action item tracking in general, and have a discussion about the items on the list. Point out how the dates seem to move and why that's a problem to the project. Review together whether the existing items appear important enough to be tracked like this. Who will benefit from the action being completed (who is the customer of the effort) and how will getting the action completed benefit the project? Review each item, toss those that don't pass the need test and assign priority to those that do. End the meeting with a statement of commitment from everyone as to how the team will use the list. Make sure they feel they can speak up if they think the list goes awry in any way in the future, or if their workload is causing them to not keep up, etc.
Then, to recover ground on the actions that are already late, and as general practice going forward, hold the assignee accountable to report to the customer when an item isn't completed on time and what barriers stand in the way.
Avoid the temptation to simply overwrite the due date with a new one. Keep all the dates on the list—the original due date plus any reset due dates—to keep visibility into how many times the task has moved. Some teams go so far as to color code the final end date (when the action item is actually closed): green if it was made on time or early, yellow if it was completed within a week of the due date, red if it was completed more than a week from the original date. This coding simply gives the team a quick visual on how they're doing meeting those dates.
Finally, do address continual slips, whether they're due to someone's overload or truly could indicate lack of commitment. In either case, it would be worth a one-on-one discussion to assess what's really going on and bring the issue to a team member's manager if needed.