You need someone to say 'no' to all the stupid ideas, and also to the occasional good idea to stay focused. Committees and communities are quite bad at that. IME the BDFL model has mostly worked best for open source software development, unless the BDFL is a complete ass of course.
(also software projects don't need to be democracies, e.g. people won't starve or sent to the gulag if things go sideways)
(also software projects don't need to be democracies, e.g. people won't starve or sent to the gulag if things go sideways)