its usually on the 1st half of the year, and yeah probably too many scandals and the office had no time to plan for 1.
but definetely not because of the lack of interest
I seem to recall sports festivals generally happening in the autumn. Though there have been some exceptions in Hello! Project, with two of them in March, I seem to recall most of them happening around the end of the year.
According to wiki:
Hello! Project Daiundōkai (March 31, 2001 at Saitama Super Arena)
Hello! Project Daiundōkai (November 3, 2002 at Osaka Dome)
Hello! Project Sports Festival 2003 (November 16, 2003 at Osaka Dome)
Hello! Project Sports Festival 2003 (November 22, 2003 at Tokyo Dome)
Hello! Project Sports Festival 2004 (November 14, 2004 at Toyota Stadium)
Hello! Project Sports Festival 2004 (December 5, 2004 at Saitama Super Arena)
Hello! Project Sports Festival 2006 ~Hello!Diva Athlete~ (March 19, 2006 at Saitama Super Arena)
I'm not sure why some of those are doubled, but maybe they decided to make it biennial since 2004?