Actually they do, just in combination with other ways of granting citizenship. To pick Italy off your list, if a child is born in Italy and it’s parents are unknown or unable to transfer their citizenship(stateless, unknown citizenship etc) the child becomes an Italian citizen. Most modern first world states provide pretty solid protections for children born on their soil.
We’ll presumably all those children born to immigrants in the US who are automatically citizens aren’t added to the “immigrant numbers” like they are in Europe?
That changes the political and migration dynamics significantly.