People also as a rule don't wear much in the way of colour either, even with cars few have bright colours
Society as a whole is drab
Muted colours overall are percived to be mature/serious, which I think a lot of people aspire too
You see it in architecture, too. Many stores are bland in color, and those that used to have more ornate logos have gone for things more minimalist in nature. Examples include:
The old one was more typical of stores opened in the 80s & 90s. My first job was at a Walmart opened in the late 80s and it looked just like the one in the top picture. The bottom picture is of the new Supercenter that opened last month at the other end of town. It's just a big, brown, flat, geometric monolith near Exit 5. Also, Walmart's logo went from a cheery smiley face to a hollowed-out asterisk.
Our local mall (yes, we have a mall that's both open and thriving, apparently a rarity these days) was opened in 1978. It had an ornate butterfly motif as its logo, seen here on the left side of the facade:
The mall was renovated and expanded in 2006-07, and now it has... this thing.
It's a flower, I guess. The mall itself lost a lot of its old character during the remodel as well. The new tiling, lighting, etc., looks so nondescript.
It seems like the 80s & early 90s had a stronger emphasis on stylized designs and bold, contrasting primary colors, and malls and arcades often had colorful neon lighting. Today, everything seems more dull, muted, and minimalist, a world of glass, steel, flat earth tones, and simple geometries. It's like we're becoming just one big transnational Apple Store.