IE6 stagnated after MS won the browser wars. It didn't get an update for like 6 years. Chrome has become a monoculture too but I think it's one of another kind.

IE6 stagnated because that was ideal for Microsoft who was mainly in the business of desktop; Chrome is now eroding user privacy and becoming a rubbish OS because that is ideal for a Google's Ad revenue and web based business. It is the same.