With millions of users and a built trust and confidence, piggy bank grows more reliable stemming from a likely good profit margin.
Ever wonder how they keep up with such interest rates( though this has be changing recently).

1. Large customer base and more savings
2. Piggy break fee of 2.5 percent( since Nigerians can be indiscipline)
3. Minimum withdrawal of #2000- meaning a lot of people have money trapped with them and lazily abandon it
4. Not trading in kobo. - many transactions leave behind kobos which amount to a lot of money that can't be claimed.
5. Dormant accounts with littered funds.
6. Dead account holders have funds laying around.
7. Traditional investment of users funds into national and international markets( or possibly crypto)

Hmmm �