I always thought that the top talent is actually leaving Germany to seek better opportunities elsewhere (already since 20y+). Main destinations Switzerland, UK, ...
Aside from FAANG and Fintechs, I don't think that London is that much better than Munich or Berlin, especially after rent. The rest of the UK was really bad salary-wise.
Germany, (and most european countries in general) have far more local levels of distinct cultures (dialect, traditions, community etc). People do not easily want to leave the place they grew up in.