I can’t speak about what the internal Church discussions about the excommunication were, hopefully someone else can.

I can add some information however:

The Catholic Church did do some excommunicating for being a Nazi leader, but it doesn’t appear as if Goebbels was specifically excommunicated for only that.

First, a some background:

Church excommunications of Nazis began in September 1930, when the bishop of Mainz excommunicated every Catholic member of the Nazi party in his diocese, banned uniformed groups from entering churches, and forbade Nazis from taking part in services and ceremonies.

In February 1931, the German bishops had their annual conferences and and decided to support the bishop of Mainz, but limited excommunications to Nazi leaders and activists, and exemptions “followers” who might have supported the Nazi Party for specific policies and without understanding the Nazis’ ultimate goals regarding religion.

In December 1931, Goebbels married. This was the time of his excommunication. While he had considering becoming a priest while younger, by this point he was already quite anti-Christianity, especially against the Catholic Church.

The Church eased its restrictions on Nazi party membership in 1933, at first to accommodate a law requiring all civil employees and union members to be party members, and then as part of maneuvers with the Nazis; cumulating in some public assurances by Hitler and the Reichsconcordant, an agreement signed in July 1933 between the Catholic Church and the German government ostensibly preserving the rights of the Church in Germany (note: Hitler became chancellor in January 1933, and seized full power in 1934). Some Catholics even helped Hitler take power, most prominently Franz von Papen.

With all of this in mind, while his own anti-Church rhetoric and string Nazis ties may well have been preexisting “strikes” that attracted Church attention, I do not believe they were the only reason Goebbels was excommunicated and here is why:

1. His excommunication was not during the general “we excommunicate Nazis leaders as a whole” time of February 1931. His excommunication occurred in at the time of his marriage, in December 1931,. It wasn’t explicitly lifted with the general ban in 1933 either, not even when the Church wasn’t excommunicating Catholics like van Papen for enabling the Nazis to take total power.

2. Geobbels wrote in his diary that he was excommunicated for his marriage, at the time of his marriage. He published an edited version that diary in 1933 before the Nazis took power and when they still the Catholic Church could have been a strong opponent, and then later had all of his diaries processed for posterity, so it is possible that he lied to maintain the fiction that a good Catholic could be a Nazi, but the original, handwritten versions remained, and were published in 2004. They say the same thing.

3. No other major Nazi leaders were excommunicated by name, not even Hitler. Some argue he doesn’t count as he had already made himself an apostate years before so the Church considered him not to be a member, but no one else was excommunicated by name either. If the only reason Geobbels was excommunicated was his Nazi leadership, then why weren’t other Nazis treated similarly?

4. His marriage was going to cause trouble. Catholic canon law from 1917-1983, specifically canon 2319 ​​§1, 1°, said that marrying, baptizing a child, or teaching a child in a belief other than Catholicism was cause for automatic excommunication. Goebbels married a divorced Protestant, who was only a Protestant herself because she was a Catholic apostate who converted to Protestantism to marry her now ex-husband, in a civil ceremony filled with the leaders of an anti Catholic party, but no priests. This was enough for automatic excommunication, and the high profile of the wedding meant that the Church was sure to know about it.

So why didn’t the Church excommunicate more Nazis?

It is very late for me, and this is in an entire question itself, but the extremely brief answer is that there are two ways to be excommunicated. One didn’t apply most of the time and the other wasn’t worth it to the Church leadership at the time.

The fast way is the automatic way (latae sententiae) that Goebbels did it. Break the wrong church rule, and you get automatic excommunication the moment that you do it. Perhaps there may be some paperwork after the fact, but that is all that it is. You are already out.

Not a lot of what the Nazis did the the pre-war years were covered by these rules. They focused more on internal church matters.

The other is by trial (sententiae ferendae). This is rare, and the existing canon law didn’t apply perfectly to what the Nazis were doing.

Of course it could have been done in some form, as the 1930/31 decisions showed, but the ultimately failed efforts to maintain Church independence in Germany and some ambivalence about some Nazi policies by some in the Church made it not Really Worth It until it was way too late. Then, the war was on, oppression was already great, Hitler’s ally Mussolini was also a strong church supporter at home in Italy and couldn’t be pushed too far, and then after that, the war was over.

Die Tagebücher von Joseph Goebbels, Aufzeichnungen 1923–1941, Volume 1, page 189

Scholder, Klaus, The Churches and the Third Reich. 2 vols. Fortress Press, 1988

Bonney, Richard, The 'Kulturkampf’ Newsletters, 1936-1939, Peter Lang Ltd. 2009

Code of Canon Law, Vatican.va