Friedrich Merz (the populist, far more aligned with CSU) and Armin Laschet (the less than competent and charismatic chancellor candidate) happened. But mostly Merkel leaving happened.
Merkel was extremely popular with the voter base. Not letting her run again was considered an extremely bad take in the CDU/CSU. So she was chancellor for 16 years. She is a consensus seeking politician without too much hard convictions, but being in coalition meant that a lot of her work put her pretty far left within her party (in absolutes, probably slightly right center; she still voted against gay marriage).
The new CDU/CSU lives mostly in the opposition and the only voters they have left to molilize have run off to the AfD, being unhappy with Merkel (and a lot of them have simply died). Most Merkel voters moved on to SPD or even Greens; the only thing that kept them with the party was Merkel as a person.
Are they really as incredibly xenophobic as the AfD?
Angela Merkel was from the CDU/CSU, and she massively expanded asylum in Germany.
What happened?