It's not about being lazy, it's about having better things to do than second guess which arcane combo of volume/home/whatever buttons is going to silence the phone. The volume switches already mean different things in different contexts (volume of music, volume of alerts, declining an incoming call...), and the home button does about a million things as well, from unlocking the phone to initiating Apple Pay to Siri, to... you get the point. And neither of these can tell you its state in a tactile manner in the dark or in your pocket. Think about it: many of the times when you need to silence your phone are the exact times when you maybe don't want to take it out and fiddle with it.
The switch does this perfectly. It does ONE thing, does it consistently, and it's self-evident which state it's in.
Ahh, ok, I didn't realize. There's this thing you can do called "not using your phone", and it's pretty great.