Many financial experts would even further argue that it's the sign of a competent treasurer if he can make the assets entrusted to him multiply with reasonably risk-free activities 
...
...Really? Multiply the assets for himself, or for the one who has entrusted him with the money?
As for banks et al. that usually entails them sharing the returns with the depositors' and they provide other services your average treasurer safeguarding other peoples' money won't provide.