The market is large enough, the transactions are relatively large, too.
In Kenya, M-Pesa is by far, the #1 payments service, with nearly half the country using it. It grew acceptance as a replacement for the other way of remitting money from the cities to villages - busses. Prior to M-Pesa, bus drivers would act, for a fee, as money carriers, bringing income back from the cities to families back home.
The competent hackers were, literally, brute-forcing the old system. Bus drivers are easier to compromise than mobile handsets and infrastructure.
In Kenya, M-Pesa is by far, the #1 payments service, with nearly half the country using it. It grew acceptance as a replacement for the other way of remitting money from the cities to villages - busses. Prior to M-Pesa, bus drivers would act, for a fee, as money carriers, bringing income back from the cities to families back home.
The competent hackers were, literally, brute-forcing the old system. Bus drivers are easier to compromise than mobile handsets and infrastructure.