The short version is that Röttgen while being seen as one of the younger coming men of the CDU and a close ally of Chancellor Angela Merkel, decided to take up a post at the Federation of German Industries. In many other countries this exchange between political and organisational careers are part of modern politics, but in Germany there still is an expectation that people will only have one career.
At the same time, critics of Chancellor Merkel could claim that Röttgen followed the lead of Friedrich Merz who were effectively pushed out of office by Merkel.
So, Röttgen’s move was interpreted as yet another sign of internal unease in the CDU.
At the same time, Röttgen was heavily criticised for wanting to keep his seat in parliament and thus sit on two chairs simultaneously: As parlamentarian and as lobbyist. In the end, he decided not to take up his post at the BDI but what effects this will have on Röttgen’s political career in the short and in the long run remains to be seen.