First of all, Spain didn't have that much population to occupy, the Spaniards came to North America in the sixteenth century, when Spain only had 8 million people, this population is not enough to plant the land in the mainland, why bother to go to the Americas to plant the land? There were no people on the mainland, so what if France came over?

Secondly, Spain is a southern European country, and Spaniards love the warmth of the sun. Most of North America, especially the eastern plains, has a very cold winter climate, something the Spanish are very unaccustomed to; and the eastern plains don't have resources that are worth too much, so the Spanish won't settle for farming.

The Mexican highlands had a cool summer climate and large deposits of gold and silver, which were highly valued. With the small number of Spaniards who made it to the Americas, they were left to concentrate their attention on the mining of precious metal deposits in the American highlands, and not so much on farming in the eastern Great Plains.

After all, what's unacceptable to you if you dig for gold and your neighbors farm? If you don't accept it, you have no place to buy food with your gold, and is that really good?