It really ought not to be though. I get that the reality is that it is but it irks me greatly that we don't simply tax more heavily and have a social system which works to solve the types of problems that charities aim to solve. Then if you wanted to do "charity work" you'd just work for the government.
I think it does not work for the same reason Soviet-style government-planned economy does not work. The incentives of private persons and of government officials are unreconcilably different.