What do they hope to achieve with this?

Have you read the article ? Here’s two articles from the STJV website with their demands, translate at your convenience:

• https://www.stjv.fr/2025/02/gg25-greve-generale-du-jeu-video-quelles-revendications/

• https://www.stjv.fr/2025/01/gg25-greve-generale-du-jeu-video-pourquoi-pour-qui-comment/

It goes further than your oversimplification ; i don’t know where you live but in France workers have rights that they fought for thanks to unions and collective actions like these, and quality of output is not the sole metric to “deserve” just pay.