Way more gold spent than earned

I have seen a few discussions on this but no one seems to be sure. Here is another case of two players on the opposing team spending significantly more gold than they earned (Sion and Ahri). Has there been a reason determined why? (PS. I was Zyra, the most macken gal playing ;-). )

http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1979104421/226951684?tab=stats

Kixx