1) The keyword is a bit off-topic so you are getting a lot of clicks from people who are not actually interested in what you want them to do.
2) Your ad is enticing to get them to click but not descriptive of your offer or service so when they get to the landing page they are confused.
3) Your landing page itself is not properly closing the deal.
Certainly you could worry about CPC, but I would worry about getting conversions first. If it does not convert your CPC does not matter.