Hi, I am Ann, a business coach with lots of experience in the field of marketing.

In your case, I have only 1 explaination.
"Facebook has high responsibility for your success!"
This means that although Ad 2 has less clicks, the real quality of one click under ad 2 is not as good as that in ad 1.
For example, in the 2nd campaign, when your customers click on your web, they spend less time reading it. Hence, the ROI will be lower in Ad 1. Facebook knows that and charges less.

Hope you are happy with my answer.
If you have any question related to marketing and business strategies, Ann is here to help!

Have a nice day.