At the time, computing didn't have the market penetration it has today. In other words, even if IBM and Microsoft had 99.9% of the market (which they had not), it didn't matter because only a tiny part of the population had computers at home and even less so in their pockets. Today's internet penetration is way bigger, almost anyone at least in the West has either a phone, laptop, tablet or desktop with a way to access Google and Facebook. Won't just go away as easily.