The contention is that people want to leave in part because of high immigration. Germany is not like America. Everyone is entitled to generous social benefits. After many years of high rates of refugee admissions (especially following the Syrian Refugee Crisis), the national budget is becoming very difficult to balance. Taxes continue to rise for everyone, and services are harder to get. Even visiting the doctor can be very difficult now in many cities. Many GPs aren’t taking any new patients. Many young Germans argue that the social contract is broken. The state prioritises the welfare of new arrivals and the elderly, and ignores the needs of the young.

Of course there are also many other factors. Germany’s decision to prematurely shut down its nuclear reactors will go down in history as one of the worst political and strategic decisions in history. It caused electricity prices to skyrocket and has decimated Germany’s previously impressive manufacturing sectors. They also have cultural issues embracing technological efficiency improvements. Most government departments still run by fax machine (by law). Most paperwork must be handled physically. Most Germans still prefer cash. Etc.

Ultimately I agree with you directionally - provided Germany liberalises its immigration only for high earners. This has been the major contention. A very high number of immigrants are low or no skill, and cost the state an enormous amount. This is causing massive economic and social issues. If Germany halted all low/no skilled immigration, sentiment would improve for high skilled immigration. Young people might feel like the social contract were not being torn up.

Edit: the level of discussion here is worse than anything I have ever experienced on Reddit. All replies are some variation of “nuh uh.”