How can scammers have so many phone numbers.

I started getting the “UNITED STATES “ calls 1 1/2 years ago 6 months after I went to a smart phone first it was just once in a while now it is daily and sometimes 2,3 times a day I never answer always block, They get another #.
Is this a company,group,spy’s….? Who are these calls coming from? Is there no way to tell it should not be tolerated.