It's a chilling strategy because the costs of not using a GPL software is always less than a legal fight.

Also, you do have rather established legal definitions of 'collective' and 'derivative works'. See, for example, Laurence Rosen: "Open Source Licensing". Then, why does the GPL3 not use them? Instead, is uses 'work based on' IIRC. So, why's that?

In my opinion, the resulting (legal) uncertainty is intentional.

Another reason: If the interpretation of the FSF is true, all works that ever linked dynamically against a Microsoft library would be derivative works of said library. Does it makes sense that companies like Adobe try to build a business on such shaky legal grounds?