Ctr is 5.21% but still high CPC and few traffic

I'm newbie in Facebook campaign, I create a "increase web conversion" campaign, target 180K people, Optimization for Ad Delivery by conversion, bid by manual 10$ per conversion, only advert on mobile news feed, although the ctr is high 5.21% I still get high CPM and CPC, and I can't get much traffic, should I change a optimization method?
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