For cars I assume one factor is resell value. "Neutral" colours seem to appeal to more people and thus selling a bright yellow car will either take you longer or won't get your as good of a price.
I have been buying bright red and yellow cars for over a decade now (no problem reselling them, FWIW). The problem is that it is so hard to even find cars for sale from the manufacturer in bright colors.
I think our tastes are being directed by marketing and bean counters making "safe bets". I feel like we've been driving office beiege for a few decades now.