I switched to Chrome when it was relatively brand new for a lot of reasons:
1. It was fast.
2. It was more stable than other browsers because it ran in multiple processes. One web page could crash without taking down the whole browser.
3. Revolutionary ability to drag tabs out of the window where they were created.
4. Address bar combined with search bar was really nice.
5. It was updated often, adding improvements and features.
Now pretty much every browser has all these features, in most cases because they are built on the same roots as Chrome. The only major browser that is completely separate is Firefox.
Anyway that wasn't always the case. These features made Chrome pretty much the best browser there was for quite a long time. So a lot of people gradually switched to it and stick with it to this day because they haven't had major problems with it.
Also, Chrome started coming pre-installed on Android phones. Or kids get a laptop for school and it has Chrome OS on it. These have good integration with the desktop Chrome, for things like shared bookmarks and history. It becomes more trouble for anyone to switch to a different browser when they have to do it on all their devices, set up new accounts, transfer their bookmarks, passwords, etc.
Also, the anti-Google politics are a relatively new thing that I don't give a crap about. So I keep using Chrome.