According to Android Beat Google is trying to redesign its Wallet service to better compete with its newest competitor, Apple Pay. The biggest hurdle, according to the article, is the amount of partners that it has to deal with. Google has to contend with the fact that its operating system is used by many hardware manufacturers that customize the Android OS and some that even have competing mobile wallets, like Samsung. Apple does not have this problem because all their hardware is made by them.
Another problem lies with the carriers who regulate the way the phones they sell work. SoftPay (formally Isis) was a mobile payment platform developed by AT&T, Verizon and T-Mobile to compete with Google wallet. The carriers went so far as to disable the NFC secure element in phones to push their SIM card based solution.
Google has a challenge ahead as it ties to pull all of their partners together to push Google Wallet to a more mainstream presence.