People will understand the words even with imperfect pronunciation which varies across a country, and I don't think B1 tests for this. In German the certification for B1 is basic to achieve even for people from different language families (alphabet familiarity is a big plus) especially if they already speak English.

Countries expect basic proficiency in the local language because they expect new citizens to integrate, not create isolated bubbles. At some point having a large mass of citizens unable to speak the local language starts being a burden on the whole society. They go to the hospital or to the authorities where they have to be provided with a service, and then it becomes a problem for the ones having to perform it.