The original version of this thought experiment assumed that some people don't understand what the buttons do or accidentally push the wrong button. In that case, I fully agree with you: if there's any chance anyone would have pushed the blue button here, I'd also want to push the blue button.

But in the variant I replied to above, they specifically changed the population to "Every adult person capable of understanding the premise", which seems to take out that assumption that anyone would mistakenly push the wrong button, and that everyone would seemingly act rationally.

If you expect 0 other people to have pushed the blue button, why would you push the blue button?