The reason apparently comes down to the political unrest currently erupting in Thailand, where the race was to be held for the second year in a row. Although the protests have been an ongoing phenomenon since 2010, last year's event in Bangkok was apparently unaffected. However an escalation of violence between protestors and government forces has apparently left the Sports Authority of Thailand with little choice but to shut it down.
In the brief statement below, organizers say they are looking at potentially moving the race to another date, but that would likely depend largely on political tensions calming down.
The Sports Authority of Thailand and the organisers of the 2013 Race Of Champions have announced that the event cannot take place as planned on December 14-15 due to the current political situation in Bangkok.
Our thoughts are with the Thai people during this difficult period and we wish that a peaceful solution will soon be found. The Race Of Champions has been held all over the world for 25 consecutive years and we are currently looking at options of repeating the success of last year's event in Bangkok on another date.
Fans who have already purchased tickets for this year's Race Of Champions should contact Thai Ticket Major or their ticketing agent for further information on refunds.