In business-speak it's called "switching cost". Google aggressively pursued the entire tech stack: search -> browser -> OS (and in many different verticals) so

In business-speak it's called "switching cost". Google aggressively pursued the entire tech stack: search -> browser -> OS (and in many different verticals) so that switching to another platform would be costly (in terms of time and convenience). That's why they branch out into so many free areas like Email, maps, etc. to create an ecosystem that works efficiently with itself and not as efficiently with external services.