The plans for the series were still unchanged after Carranger, it was decided that they wanted to do an episode where Basco stole the Great Power of a team. Since Basco has the Black Knight Ranger Key, they decided to do a Gingaman tribute.
Around the time Ogawa was offered the reprise his role as Black Knight Hyuga, Japan was struck by a killer earthquake and he made the Tokusatsu Hero Twitter account (@tokusatsuhero) wherein past toku actors send tweets to cheer people up. The account received a lot of publicity and messages from other Sentai vets, which made a lot of past Sentai actors to be aware of Gokaiger.
They started receiving a lot of calls and messages from actors and even retired guys who found out about the show through the toku Twitter or other means to let them show up in Gokaiger. That's the reason why we have a lot of tribute episodes after the Gingaman episode. Producer Utsunomiya credits the online involvement of Black Knight Hyuuga and GingaRed for drastically changing Gokaiger.
In short, most cameos was an extremely last minute thing. Basco stealing the powers was because they needed the villain to succeed in stealing powers and as insurance just in case they couldn't get those guys back and the Zyuranger Great Power was obviously already taken care of.
In short, the additional floating heads of past Super Sentai heroes are just last minute additions since the movie already finished its filming. You also have to remember that the audience of late teens/young adults who started watching Gokaiger because of returning actors are of the 86~94 range, which is why pretty much every team after Liveman had a tribute.
To put it simply, without Ogawa and Maehara's involvement with the show, the only tributes that the show will have are: Magiranger, Dekaranger, Gekiranger, Gaoranger, Shinkenger, Carranger, Gingaman, Hurricaneger and Go-Onger.
Source: Red Ranger of HJU via Low Visibility Podcast
Originally posted on Orends: Range back in October 11, 2012.