Same question has been asked a lot. so far i can say these reasons:

1.big amount of premine always raises questions and people tend to not trust the project.
2. 12M SUDO will minted in 1 year in highest block reward period. premine/minted ratio is way off.
3. it would affect our stats badly like locked coin percentage, marketcap etc.
4. it was locked to support platform contributers but fixed amount is not enough and not a good choice. creating an income stream is more logical in the long term. we will try to do that.
we can still lock some amount to support platform at beginning but dont need 9M for that