I remember using opera a few years back when smartphones had hit the market for the first time. I was using Sony Xperia Mini. It had an inbuilt (already installed) Opera browser app. I didn't use any other browser, though I was familiar with many other browsers. If I recall it correctly, it had a neatly organised user interface and I was completely happy with the experience.
But, the shift happened when I started using the laptop and changed my phone. Laptops have Google chrome as a default browser, and smartphones running on android OS gives us chrome. I think the shift happened more like an external force. When people start using smartphones that run on android, they get used to the idea that chrome is a default browser. The majority of the users do not download or install any other browser, they will never go to that extend and they stick with what they have.