If you are wondering why he chose Barcelona and not Chelsea or Paris SG I already answer. Lewy wants to win trophies. Seeing that he only won the Champions League once in 8 years at Bayern is a failure for him. He criticized Nagelsman a lot after the match in which they dropped out. Paris SG - he would be one of 4 (Mbappe, Messi, Neymar) and a weak league. Chealsea, Robert is fed up with the weather in Germany (12 years he played there), he wants sunny Spain. On top of that, it's very possible that he knows Spanish, because he was very close to Real a few times. He's a professional, after 3 months of playing in Dortmund he was already giving interviews on German TV. The last reason is the Golden Ball. Lewy wants to win it finally. The Bundesliga is watched by 10x less people than La Liga.
btw. don't worry about form, he's a machine. He had 1 serious injury in his life, but when he was still a chucher - at the age of 17. In the Polish national team he contributes to 3/4 of the goals. When he finishes his career in 2-3 years, Poland will not qualify for the European and World Championships. Besides, you probably remember who scored the goal in the Poland - Spain game at Euro 2020.