What I don't understand is why the AV1 pool isn't activating their MAD clause.

Part of the idea with AV1 was that with the constituents also holding such a massive warchest of patents (plus big tech being richer than god), they would countersue and demolish anyone that tries to bully AV1 users. Which would act like deterrence.

Where is all that might? Was it all just saber rattling, and are they basically going to let the AVC / HEVC patent holders make a fool out of them?

For now Dolby has just filed a lawsuit.

If this will reach a trial, it remains to be seen whether Snap will fight alone or it will receive support.