The correct response to why tides have a regular cycle of 12 hours, despite the Moon completing one revolution of the Earth every 29.5 days, is:
The Earth is rotating and completes a rotation every 24 hours. This means that the side of the Earth far from the Moon will be near the Moon 12 hours later, restarting the cycle of high and low tide.
This explanation highlights the relationship between the Earth's rotation and the gravitational pull of the Moon, leading to the regular high and low tide cycles.