If you consider this "central planning", then you must consider all companies to also use "central planning" as the voting method is extremely similar.

1. Because serious tasks often require coordinated efforts by programmers and often the ones with the skills you need don't want to develop something then just hope they will get paid for it, when there's plenty of people willing to pay them in a more timely manner.
2. See 1 above
3. It's not voting spend other people's money: it's voting by a group of people to spend their collective money (very similar to the way normal corporations function).