The story you linked is from 2015, and has nothing to do with exit nodes. The feds bsuted the actual server that was used to host csam and kept it up while collecting user information for two weeks. Not exit nodes related.

There are many illegal sites hosted on tor that get taken down quite often. Tor in itself is not an insecure software and it proves that by readily having nefarious and illegal sites operate for long durations of time.

All the instances I have read about large sites that host some form of illegal content on Tor going down have all had quite unique and extensive efforts put in by law enforcement agencies to make the bust happen.