The party is unable to moderate because, between 2017 and 2021, it has further radicalized to the right. This is also a reason why the party is unable to grow further: It is extremely toxic and supports stances and politicians that are held in wide contempt by the German public. Those ideas and people were there pre-2017, yes, but it was an extra-parliamentary opposition party then. There sure was the expectation by some that once the party has entered the institutions, it would moderate and learn how to play by the rules. It did not, and so the party is very uninteresting for many German voters: It is a right-wing party which has become so extremist and possibleyunconstitutional that German intelligence agencies are deliberating whether it should be surveilled (as some state branches already are!), they are utterly unable to produce a coherent policy proposal because there is deep party infighting, and they can't even get stuff done in parliament.
It's telling that Bernd Lucke lost a power struggle in the party to Frauke Petry back in 2015 and two years later both of them were out of the party because it was too extreme to tolerate either of them.
