The gist of it is that an election creates a level of...

The gist of it is that an election creates a level of uncertainty in people's lives and they (to a greater or lesser extent) defer making spending decisions. This means lower retail sales, less housing turnover, less travelling etc. As a result, companies hold off on pulling the trigger on ad campaigns, which in turn results in lower revenue for media companies in TV, outdoor, publishers etc.

APO blamed the prolonged election yes, but it's likely the Olympics had more of an impact. Companies allocate more spend to TV during the Olympics and with fixed marketing budgets, this means less spent on outdoor etc.