The original main storyline of the game was completely borked with One Tamriel, and has never been fixed. It used to be fed to you 5-ish levels at a time, until you hit level 50. By that time, you had usually completed your faction's zones and met the important players.
So, when you are near the final mission, you are reuniting with characters with whom you are well-acquainted.
After one Tamriel, it became possible to do the main storyline quests in immediate succession, so you could finish them all at a low level and without having done the background content. You can get up to the final quest, and then you are "reuniting" with people you've never met.
In addition, it is very easy to miss the Hooded Figure that starts the main questline. Several people I have spoken to do not even know this questline exists - which is sad, as it explains a lot about the game.
This quest should be returned to a periodic bestowal and I'd even suggest that players be forced/enticed to complete it.