It's because people are reading the first few words and thinking "this is an male nerd asking stupid ignorant questions".
It's that or there are people who actually think that counting days is a good way to enable unprotected sex without a risk of baby. Which is absolutely isn't - it changes the risk to 2-5% a shot. Compared to around ~2% year for condoms alone.
It's worth pointing out that due to the nature of how contraceptive studies are done, it's remarkably easy to stay out of that 2% for condoms. (Namely, if you're planning on using condoms as your choice of contraceptive, actually use the condoms).
They can burst and slip off too. That's the problem. I'm anti-abortion* so we took extra measures to avoid the argument (my wife is Pro, and I although have no right to tell anyone else what to do with their body, it would probably have ended our relationship had she done it).
* For myself, I find that the Americans who try to force everyone else to follow their personal positions to be insane Authoritarian Fascists. Our society only works if people have freedom and personal choice.