[robotoloco]

The main reason was neutrality, and respect for the popular language. 'Fixing' the inconsistencies of a language means getting rid of its identity, and culture. You may be able to do that with a dead language, but not with a living one.

As for neutrality, an English or Spanish speaker would always have the advantage, thus the idea that everybody can meet on a ground as even as possible. Esperanto tried to solve that by not belonging to any people, or any nation. It ended up being Eurocentric, but to some extent it does fulfill its neutrality motivation