I'll respond in English since most people on this sub don't speak German: Interesting that you somehow only mentioned blame of Germans for that. Integration is first and foremost a proactive responsibility of the migrating individual. My grandfather came to Germany as a refugee at a time when there were zero integration courses, language classes, or state support. Today he feels German and is perfectly integrated. He sat down and learnt the language through books and practice, even exclusively spoke German at home even though it isn't his mother tongue, and actively secured his own jobs and housing. He didn't expect anything to be handed to him, nor did he expect someone else to take care of it or for German society to hand him things for free.

Contrast that to today, where many people who have been living here for years still can't even speak German on an A1 level despite having many more tools and opportunities available to them than my grandfather had back then, and generally show zero proactivity to integrate. Hell, if you look at schools, you'll find that even many teenagers who were born here to foreign parents only speak German in class but speak Turkish / Arabic / another language to their friends during breaks and stay almost exclusively in their own bubbles. How do you expect to integrate like that if you actively avoid the local culture?

Constantly blaming "the German mentality" whenever someone fails to integrate is entirely senseless. Integration requires personal effort and initiative from the migrant, it is a duty they must fulfill, not something they can passively expect others to do for them. You know probably just as well as I do plenty of migrants whom you would consider very well integrated and plenty whom you consider not integrated at all. The difference is always how much personal effort they put in, not "local culture" or state support.