I made the switch in 2013 with the 5s.
The reason I switched wasn't really the OS... or maybe it was in a way. The primary reason I switched from Android to iOS at the time was that iPhones seemed to have a much longer lifespan than the Android phones at the time.
At one point, you couldn't pay me to buy an iPhone but after about a 1.5 years of use, the Android phones became slow, laggy, and buggy. After 2 years, you were getting no updates and no support. To keep my Android phones for longer than 2 years, I had to suffer through the slowness, and the lag in response or feedback on the touchscreen. Meanwhile all my friends have their 2 year old iPhones that are moving smooth like butter. That's what made me really switch after resisting for years.
I'm not sure if that's a problem that Android phones still have.