it's because the stupidphone's stupid keyboard capitalizes for you in the wrong places, and you have to take extra effort to fix it when they get it wrong, or you turn it off, and then get lazy about fixing it when you do need the capitalization.
>>fragme+(OP)
Does it? When I start a message, the keyboard automatically capitalizes. It also does it when a sentence starts after a period. I rarely ever have to fix capitalization.