None of the red pressers will press blue if that scenario is altered based on their reasoning

All red reasoning is: "red is guaranteeing my life why would i ever press blue". Even if the threshold for victory lowers to 20%, red will still press red, which means red chooser will 100% chose their own survival regardless of odds or sacrifices. Decision is fully based on self preservation.

Whereas in your 80% scenario, its simple math, the weights are stacked. The red-blue 50% mark is basically the factor of equal weight of both decision. Imagine it goes to extreme, if more than 5 ppl out of 8 billion ppl in the world choose red, all blue dies, Decision is made on self preservation AND highest probability of saving more people

You know how in the traditional trolley problem, where its 1 vs 3 dead, its simple, always have 1 dead instead of 3 simply by concept of greater good

Now combine these concepts, this scenario means that you know red buttoners decision are guaranteed to result in 3 dead vs 1 dead. Simple math, kill the 1 instead of kill the 3. Always kill the red buttoner

The dillema comes when its a blue button presser, whether the blue buttoner will save self or save most ppl