I think the parent was asking: why do we think that people who H1B immigrants who move in will make a worse neighborhood than current "native" residents?
Ah, I think I understand but the logic still seems a little twisted. Gentrification is an economic process, so the passport of the gentrifier doesn't really matter here.
Part of the reason I was confused is because -- at least where I live -- communities with a high number of foreign born residents are actually the ones most at risk of gentrification.