That's a good question. Here is a link to the numbers:

http://thehackernews.com/2015/10/cryptowall-ransomware.html

That averages out at $800 per infection compared to about $0.30 per infection from WannaCry. I suspect there are other factors at play here (was all the revenue from ransoms? were that target systems different? are people hardening in their resolve not to pay these ransoms?).