You would think to combat birthdates you would increase immigration to an appropriate level not 10x it in 5 years.
Secondly immigration has a complicated affect on demographics since the people coming are generally 21 or older which is very clearly different than a birth which starts at 0 years old
...because of immigration? Birth rates have been far below replacement for decades now.
https://en.wikipedia.org/wiki/File:Total_Fertility_Rate_of_C...
They result in 2 very different distributions. One having a very large segment of the population in one specific age category. Which also puts a lot of pressure on systems / infrastructure that is relevant to that category.
The idea that a country must import more immigrants because birthrates are not increasing or are below replacement is just "number go up" economics. It's the same trite and annoying arguments that some Bitcoin boosters make (the ones who don't actually understand the underlying technology, there's a parallel there).
Japan, for one example, isn't going to collapse. Or should they import 50M immigrants from across the planet to make sure the numbers in the spreadsheets go up?
That's why Japan has been bringing in nurses and caretakers from abroad en masse. Unless you want to make the argument that past a certain point they should just be left to die, but given that often the people that vote the most were elderly, well...