Then again, there are alot of factors to consider right here when organising a competition. It is not really as easy as abc:
1. Amount of prizes (where are we gonna get the prizes? would there be a sponsor?)
2. Availability of suitable venues (mind you, this can be an issue, especially if you are not part of an organisation (school or commercial)
3. Logistics
For the record, the past 3 competitions in Singapore (namely, 2011, 2012 and including this year's edition) has been organised by some societal organisation in NUS, namely the NUS Mathematics Society. However, it may not be so feasible for them to organise that many competitions in a calendar year, considering that they do have a budget to work with. In view of that, we may have to look for other organisers if we want to have more competitions here.
All in all, I am all for the idea of having more competitions in Singapore (after all, I am a Singaporean), but in my honest opinion it takes more than just collective effort from the local community to have more competitions right here. There are many factors involved that you would think.