Overseas shareholders are not entitled to the imputation...

Overseas shareholders are not entitled to the imputation credit.

Or possibly some shareholders have had such a rise that they not worried about the imputation credit.

Another possibility is that they a small shareholder.

If you have a good dividend stripping strategy let me know.

Anyways here is the ATO position on stripping:

Holding period rule
The holding period rule requires you to continuously hold shares 'at risk' for at least 45 days (90 days for certain preference shares) to be eligible for the franking tax offset. However, under the small shareholder exemption this rule does not apply if your total franking credit entitlement is below $5,000, which is roughly equivalent to receiving a fully franked dividend of $11,666 (based on the current tax rate of 30% for companies).
This means that you must continuously own shares 'at risk' for at least 45 days (90 days for certain preference shares) not counting the day of acquisition or disposal to be eligible for any franking tax offset.