Back in the day, Chrome was faster — almost as fast as Safari to launch and faster when executing heavy sites. When it took IE and Firefox longer to load, installing Chrome was something which had an immediate benefit and Google's heavy promotion of it meant that most people gave it a try.

These days, I agree that the main problem is that any modern browser is good enough that people don't feel a huge pressure to switch. I prefer Firefox's developer tools but that's not exactly a mainstream need. The most obvious angle would be something about ad blocking and privacy where Google has significant financial incentives not to follow but I' m not sure how much of an audience that could add up to and it will definitely get hostility if effective.