They are unionized employees who have collectively decided to go on strike. They are likely not being paid anything at the moment. Their benefits may lapse if it's an extremely extended strike (although that would probably be unlikely).

This looks like a normal union activity: using the skills of their trade to get more attention from a wider public.

To be honest, I do have open questions about unionized approaches to labor in software-only technology businesses. But many sectors are already well established in having unionized labor. The US news media is one such sector. These are skilled professionals who are part of a union working for a large employer that negotiates contracts with a wide range of different unions. It's their right to decide to go on strike in order to secure a better contract.

(Not that not all unions are allowed to go on strike. An NYT reporter posted to BlueSky the other day that the reporter's union agreed to a contract that constrains the conditions under which they can actually strike.)

I'm not really sure what's weird. Programming is a skill -- it can be used for fun, for work, for your benefit, and/or for others' benefit.

The union does not want to work for their employer at the moment because they don't believe they're being treated fairly and not working is one of the only points of leverage a worker has. So they're using that leverage.

Why would that prevent them from working on a fun game or project to help further their cause?

A strike does not mean they don’t want to work, they are withholding labor as leverage for collective negotiations.

Many developers, often the best, program for joy not [only] money.