Why did us lawmakers not feel the need to begin restricting immigration until 1875?

the U. S. lawmakers immigration numbers were not increasing rapidly then

Explanation:

Before 1875, most of the lands in united states were not occupied. Which is why they considered immigration as a good things since they need more people to come into the country and take care of the resources.

Beyond 1875, The lands started to became heavily populated. Many people all across the worlds wanted to come to untied states with the hope of achieving freedom and obtaining more economic opportunities. The number of immigrants become larger than the amount of resources available. This created massive competition in the country.

So, Lawmakers started to restrict the number of immigrants that can come into the country.