People aren't rational actors. This has been demonstrated in many econ experiments. Tax is a pain that is reoccurring. The government even reassess the value of your land periodically. Many people don't do this and may not know their land is underutilized. It is essentially a little nudge every year.

In this case, maximum utilization means maximum economic output, which is good for GDP and good for the country. It may not be the best for the local society, though. That part is hard to quantify and controversial.