great - however you are one person, the large banks involved here have staff of a few hundred thousand each across several countries and with various backgrounds and norms, many who are also friends and have contact with each other outside of office hours.
I agree, one needs to keep work comms on approved software, I'm simply stating that while it's fun to be like "oohh big bad bank was hiding secret convos" it was more likely "janet i'm out today can you take the meeting with svp of <insert corp>"
Put another way context matters in terms of how the public should react to the news, not so much the result (fines) or the regulations / requirements.
I would tell people to fuck off if they wanted to invade my personal device with work chatter. Boundaries are good