Unless I forgot one, I think I'm on my 10th mobile phone in total since the late 1990s, so averaging just under 3 years per phone. And I think the interval was shorter in the feature phone days and longer in the last 12 years or so where I'm now on my 4th smartphone.
Maybe it's because I learned to be careful with my phones before smartphones existed, back when dropping it might mean the back cover, battery, and main body flying in different directions. As a result, I'm also the kind of person who might drop his phone/wallet/passport into ziplock bags if I was heading outside with a chance of significant rain...
Same here, but I don't pretend that my experience is typical.
Even if it is, and, say, only 20% of people end up dropping a phone in a toilet or cracking the screen, it seems worth it to build in water and crack resistance.