The keyboard is actually a very intimate aspect of your interaction with your computer. For many folks this is important. Minutia about the "effect on performance" is not really a concern (IMHO if people are being honest). The real thing is how the keyboard FEELS, the sensory feedback-- sounds, tactile and appearance. It's also a way to customize something to your liking even if you're "doing a job" on the computer, much like wearing a tie of one's choice gave corporate workers an outlet for some individual expression back in the day.

I doubt anyone "argues" about keyboards unless they're being forced to use one they don't like. And most folks can do just fine on a wide variety of keyboards-- although the really alien-ones like the Atreus and those hipster ortho's necessitate a learning curve and motor skills development.