It looks like they are proud of their country and want to keep it as is. They’ve seen what limitless immigration did to other countries and want none of it. Respect to them.
Japan is worse.
you can piddle around about a few tiny islands elsewhere, e.g. okinawa, but the main islands are undisputedly "japan"
Japanese population is still over 120 million. Forecasts put it falling below 100 million at some point in the second half of this century.
Things will have to change in order to keep population stable in the long term, but the Japanese approach seems IMHO more sensible than that of other countries.
Cohesive democratic societies are fragile.
The birth rates of the immigrant waves would presumably just plummet quickly anyway as they join the culture. Since that seems to have happened with all our other health problems.
Emphasis on slightly younger. Fertility is declining basically everywhere. Much of the developing world is now below replacement including India and China.
The aged society scam can only persist as long as they can exploit the younger generation. When that collapses, the end result is either going to be leaving the elderly to die or things start collapsing in new and interesting ways
The only reason why people 'prefer' this is for the same reason 'prefer' to believe climate change doesn't exist. Eventually reality catches up.
Immigration is not a long term solution to an aged society. The societies of target countries are aging as well and not far behind.
What you advocate is to bolster the work force of a country with a fertility rate of ~1 and falling, with people from a place with a fertility rate of ~2 and falling.
But none of the german, french, italian etc politicians have the balls to let society decide for themselves, controversial topic or not. And people then wonder why in extremely left-leaning country like France there is high popularity for extreme right parties.
Maybe british with their one self-kneecaping brexit vote cured them, but public voting in general was never on the table.
Swiss are the most free nation globally. At least I havent hears of any on similar level. They vote responsibly, heck they have 3x the amount of immigrants per capita then next top country in Europe, but they want only people who can find work there, plus they host tons of refugees. And yes they dont want to lose their unique identity, they have enough examples around them to be wary and smart. I'd say they do their share and some more