What is the reason for such a dramatic fall in CDU/CSU popularity and an increase for SPD? Also Greens lose voters, while SPD does not – why? I am non-German and intrigued by this (especially first question).

What is the reason for such a dramatic fall in CDU/CSU popularity and an increase for SPD? Also Greens lose voters, while SPD does not – why? I am non-German and intrigued by this (especially first question).