Most deep-space probes use storable hypergolics (hydrazines + nitrogen tetroxide). Some of the crazy parts of this book actually came true!

(I don't intuitively understand how the JWST has $10 billion precision optics and hypercorrosive oxidizers right next to each other, and nothing bad happens. Engineering baffles me).

Those experiments generally needed to be run to figure out what was possible and what the different realistic options were, though. There's also more uses for propellants than just orbital launchers; propellant for ICBMs (and other strategic missiles), thrusters for attitude control, some of the monopropellants can also be used to power APUs for hydraulics or electricity. But yes, most applications these days go with simpler, more stable fuels, especially for commercial companies that don't want to spend a bunch of extra money wrangling more sensitive fuels for a few extra seconds of Isp.