As Saul points out above it’s only a minority of Ryanair that’s unionised. Not enough to make it count in a situation like this. The french bases are mainly crewed by Air Malta so they are not represented by SNPL as far as I know.
There’s a lot of reasons the unions haven’t been successful with Ryanair. Main one probably the tactics of Ryanair always keeping them one step ahead of national legislation and local unions. On top of that the whole self-employment issue with everyone employed differently.
I don’t agree with their practises but they are very good at what they do. And yes this is not the time to fight without the protection of unions. I completely agree.