The idea among the political class - both ends - has for a long time been that immigration is good for the economy, increases productivity, and all the rest. So they have pushed it and pushed it.
Actual people living in towns and such, in the UK, Europe, Canada, Australia, have been for a long time pointing out that the effects in the population aren't so rosy. It's finally got to the point that people are starting to push back politically in a serious way.
Even here in Canada the national bank among others have finally had to admit that this level of immigration has actually been bad for the country economically. And it's become apparent even to the political classes that infrastructure can't keep up - people having no access to a GP for five years is a problem that is not helped by adding 100 more people per GP to the population.
In the UK there is the additional issue of space. I don't understand people saying, who will do the shitty jobs (lovely leftists looking to import people to do the shit jobs.) Even if it were true that no one would do the shitty jobs, it does not mean that adding so many more people is sustainable. Ultimately, people may have to pay more for some services, or go without some that aren't necessary if they aren't willing to pay wages that attract workers for them.
What I find really sad is the change in attitude to immigration. Canadians have always been so welcoming to newcomers, really generous and kind. Now with the masses of immigration people are struggling to find housing, certain kinds of jobs, doctors, places in schools, and their attitude is changing. Most don't blame the newcomers, but it certainly affects their general attitude.