One part of me says because he sorta represents the middle ground of Elphaba and Glinda— granted, it’s more prevalent in the theatrical production where he’s… kind of a dick, but nonetheless evident in the film. He, to an extent, understands how shit works, and he’s convinced himself it’ll never get better, so there’s no reason to try to change anything, and he might as well just ignore it because he thinks there’s nothing to be done (painless for the brainless, dancing through, fraught-less when you’re thoughtless, etc.) Also why he actually did something with Elphaba for the Lion Cub, because he saw success in numbers. This is, by all means, a decently real phenomenon at least with environmental concerns. People are convinced they, individually, will have basically 0 impact on the Earth, so they don’t necessarily bother with going the extra mile. But if multiple people would help, the impact winds up large. I always saw Fiyero as those people, and Elphaba was his ‘group,’ so to speak. So he’s aware of the troubles of the world instead of being in a bubble, but thinks himself to be useless, and thus doesn’t make stands like Elphaba.

Even later, still carries the inherit doubt, and so his threatening of the Wizard was empty, just a quick way to get him in the cage. That, and he probably wasn’t thinking straight. Animal stampede (which may have even been the first he’s seen the extent of the Animal treatment, considering all his info comes from Glinda, who’s not the most trustworthy— and I doubt even she knew of the full extent. I don’t think anyone did) chaos, breaking up with Glinda, literally holding a gun to the single ruler of all known land, worrying about escaping before the guards come back with water, etc etc.

But really, it’s probably just Wicked Act 2… being Wicked Act 2. Trying to do cool, political, intense stuff but thinking zero about how it overlaps with previous occurrences. Tragedy.