[1] Many people buy phones on loans, because even cheap phones are quite expensive for the average Kenyan.
[2] These phone companies _already_ use device policy based apps to control usage for those who have not paid. The difference is that these apps are actually predatory, they are free to siphon off data and what not, and have the usual shadiness that you expect from apps made by relatively random corps who care way less about user privacy than big cos.
What this solution seems to be doing is providing a way to enforce the device lock policy at the OS level that actually lessens the vice-grip that these companies have on the user's phones and limits the power of the company to only block the phone from use, as opposed to the earlier model where they could do whatever the fuck they wanted on the device using their installed software.