While a simple solution for a popularity contest, it has great drawbacks when looking for techique comparison. Someone's family may be bigger or louder than others, some people may have more fans in the audience, who can afford to attend will skew the vote, being an international event would mean that it's likely the home team has the advantage as people from the host country have a greater opportunity to attend, some event crowds may be determined by time of day or by public transportation, and the audience may not see the whole (5 hour breakdancing) event and certainly won't see the performers as well/as close as the judges would. Additionally the audience has so many new viewers during the Olympics that don't know how hard certain moves/sequence of moves are while some easy flashy moves will wow a crowd every single time. None of those things show particularly compelling qualification to determine how technically good the performer/performance is.