Thanks for your response! You are making an assumption that most or all immigrants wish they didn't have to immigrate. I will answer assuming this is true, though I am not confident it is. But let's go with it.

Changes in material conditions of a country typically occur due to political action. That may be in terms of voting, political movements, or outside forces like war or sanctions. Addressing each of those:

1. Immigrants typically can still vote, so no issue here
2. immigrants are unlikely to affect political movements when they are immigrating for reasons like work, study, reuniting with other family, or enjoying lifestyle of another country.
3. Immigrants have little to no effect on wars and sanctions.

And last, even if what you quoted is true, I bet whoever said it is likely not considering putting the effort of making their country better in the same way they want immigrants to. Maybe that's not one of the worse forms of racism, but it is one.