Infrastructure isn’t tied directly to labour available.
There needs to be enough time to construct, enough money to invest, enough space to have proper city layouts etc.
You can’t just build a water treatment plant anywhere.
You also can only build housing and schools and hospitals so fast, an extra 100 million people in America in less than ten years would mean and extra 25% or everything needing to be built in less than ten years.
At the moment government doesn’t fund construction of housing, so that’s an entire system that needs to put in place before letting everyone in.
Plus a bunch of other issues that I can’t even think about I imagine.









Canada had an annual immigration rate of 1.4 million per year and the population is 40 million and that’s still with a limited non-open door policy, and it was way too much which Canada realized and started to restrict it, which would be the equivalent of America bringing in 14 million a year.
I absolutely wouldn’t be surprised if 100 mil wanted to immigrate to America over ten years if there was an open door policy.