The tours were longer and included games against clubs because the club seasons in England and Australia ran at different times. I went to the 1994 Australia game at Wilderspool too, and loved watching Jonathan Davies score for GB on telly. That series was in the middle of our season and after the Australian season though, so the Aussies were over on tour and the clubs here were playing league games in between the GB internationals and club team exhibitions V the Aussies.
Since 1996 the two leagues have ran concurrently, so unless you have players centrally contracted and clubs allow them to disappear on tour for two months in the middle of the season, which Super League couldn't afford and the NRL would just laugh at, then the international "season" can only ever be a tag on in October and November when most fans see the real business as being over until February and no clubs would have enough players available to be able to field a team against the touring side.