[timbit42]

One reason is that the Baby Boomer generation is nearly 100% retired now and no longer making big money and paying big income and sales taxes. This means government revenues are down, right at the same time that the Baby Boomers will begin heavily leaning on public services, particularly healthcare. Immigration brings workers, who are young enough to not need much healthcare, to replace the Baby Boomers and increases government income and sales tax revenue. It's like a Ponzi scheme they are trying to keep from collapsing. As the Baby Boomers pass on, their homes will become available for younger generations to live in.