People have been caught making bomb threats using their own phones. Some people are just not bright enough to be able to survive in this world.
It's for people like them that you have to have signs everywhere that say things like, don't stick your hand in the crushy grindy place, this hot water is hot, and don't drink bleach you'll die.
People in general really. Some of the stuff your average person does on the internet and their devices absolutely stumps me, and I'm not even that tech savvy.
Ease of use, plus people anticipate that there will be much more "noise" drowning their activities out in the daily torrent of information. Then back to your point again, people are dumb and forget it's relatively easy to lookout for certain things even with enormous data flow.