How do Bonus accounts work? You get a bonus into the bonus account. Meet the wager requirements, and then the money can be moved to your regular account? Are you then free to cash it out from your regular account?
Also remember some (if not all?) have minimum transfer into real account of $50, or the amount of bonus received.
So if you meet WR and are just $1 below this figure, you HAVE to carry on wagering - and sods law tells you what will happen!
Read ALL the T&C's VERY carefully - then try a different casino!