They have. Hundreds of thousands have immigrated here from Eastern Europe and Russia in the last decade. The problem is illegal immigration, if they would cut it off it would slow the Aztlan train down considerably.
Personally, I'd like to see a break in ALL immigration for a while, we've taken in over 35 million in the last 40 years, enough is enough.
There are tons of East Europeans who would love to immigrate to the United States. I've met them and they're solid people. They are educated and English speaking. They would make great citizens. Our immigration is way too slanted to the 3rd world and away from the Europe that built the USA. This stinks.