Considering that AI bonuses become strongest during that period, and that the biggest swings in war/diplomacy can happen when ideologies emerge, forcing a cultural victory player to 'stick it out' until Telecom is like saying that a science victory player is forced to 'stick it out' until the end just because they have a 5 tech lead in the modern era. Your influence may dwindle somehow, and this forced window of time gives other players (especially diplo players) time to mess with the late-game resolutions and tenets to muck with your lead. It also lets the AI coalition-build a little more reliably. All in all, I think your impression of victory needs to adapt - you don't win until you see the splash and - until then - other players have a chance to bring you down or win on their own.
G