Every recreational sailor knows that AIS is "mandatory." It's completely routine to see commercial ships running without it.
> It's completely routine to see commercial ships running without it
I think this depends a lot on the location, as different areas seems to make it different levels of "mandatory". Are you speaking about the Baltic Sea specifically based on experience?
With "commercial", I guess you imply fishing vessels doing this to go fishing outside their delimited area. That's different from a massive bulk carrier in the middle of the Baltic