Are most pregnancies on pill due to people error or is the pill just not effective?

If taken correctly, the pill is 99% effective. I don't know if there are any stats on it, but in my opinion I think people not taking it correctly probably causes most pregnancies. Most women don't take it at the right time or may miss a day here and there which will reduce effectiveness.
Erm, this is not correct. If you forget to take 1 pill it does not mean you then have a 100% chance of pregnancy. Please don't give out information like this because it is scare-mongering and will cause unnecessary worry to young vulnerable women. Even if you have completely unprotected sex, there is not a 100% chance of pregnancy. There is never a 100% chance of pregnancy.

OP - if you're on the pill or wanting to go on the pill, take it at the same time each day and do not miss a pill and you should be okay as it'll be 99% effective. Even with "real life" use e.g. taking it a few hours late, the effectiveness is around 91% which is still high, but you should aim to take it correctly all the time.