The problem isn't that fewer unusual colors are made.
The problem is that no unusual colors are made in almost all car models.
There are a very small handful of models that have a few particular colors beyond the basic black/white/red/silver/dark blue options, but otherwise manufacturers have decided that because fewer people want yellow (or bright blue, or pink, or orange, or magenta), no one gets those colors. Ever.
Even the new Miata's color options are gray-scale, red, very dark blue, and sand. Worth mentioning that you can just buy wraps for wacky colors while protecting your paint and resale value, maybe that's part of it.
The problem is that no unusual colors are made in almost all car models.
There are a very small handful of models that have a few particular colors beyond the basic black/white/red/silver/dark blue options, but otherwise manufacturers have decided that because fewer people want yellow (or bright blue, or pink, or orange, or magenta), no one gets those colors. Ever.