If you license individuals, how do you categorize what is and is not journalism, and where do you stop? Photojournalists, blogs, for fun school magazines, local newspapers? Are radio shows journalism? Youtube channels? Do I become an unlicensed journalist if they hold misinformation? Thinking of the worst case, a corrupted governing body could quietly pick and choose who they want to take penalize for not practicing with a license, or penalize them out of existence even if they have one.
That benefits big news corps while stifling open/free journalism with risk. For one example of what I mean by that but in a different industry, I will never run a website that could have users upload media in my country, because we have no safe-harbour laws. If you are at risk of penalties, many people just won't start.
The AMA and bar associations are not without their issues either (they end up driving prices up since they have a monopoly on their service), but it seems to me that people don't have to worry about doctors doxxing their patients on social media or lawyers making deals behind a client's back as much. When it does happen, these professionals are usually ejected from their profession, which is a pretty big disincentive.