why did the national colonization law did not allow foreign settlers to settle on or near boundaries and coastlines

The National Colonization Law of 1824 guaranteed to foreigners settling in Texas security for their persons and property. In order to protect the people who were colonizing Texas (colonists), the US government reserved ten coast leagues, and twenty leagues bordering on the United States from location. That was the main reason why the colonist were not allow to settle in these protected or reserved areas, for their own protection.