Because I don't know what I am saying yes to , or for that matter what I am saying no to .Yes or no is a meaningless choice .
Imagine someone asked me if I wanted a holiday, so I say yes , then it turns out the holiday is in Siberia , I am allowed no warm clothes and it will cost me all my savings.I am going to wish I had asked a few more questions am I not , and possibly If I had I wouldn't have said yes so rapidly.
Honestly people who want a yes no are the sort of people who sign things without reading them and them complain that they don't like the terms they agreed to .