It's always a combination of universality and exclusivity. The latter creates a "gradient" which causes a particular design to spread. Watch the documentary "Helvetica". At it's peak in the 1960s, Helvetica had high-end "international" aura and small brands everywhere were scrambling to redesign their signage to what they perceived was a new customer-friendly yet high-end image (probably best visualized as a smiling and good-looking Swiss airline flight attendant with a noticeable accent).