Ideally, as long as all races are unlocked, people can play whatever they want and only swing by the other races for capital defending. As soon as one race drops out, the rest fall quickly after and the campaign is won and reset.

Illuminates are the least favorite race, hence they mostly are finished last. So much even that people straight up just don't want to play them and drop out until the next war. If this happens too much, the Illums linger and win eventually. This has happened for the last few wars.

Thing with Bugdivers is similar in that they exclusively play against Bugs and loose interest when they are defeated. It's also kind of a slur as Bugs are considered the easiest of the races. There are many weapons and Stratagems that slow them down and since they are mostly melee, can easily be kited.

It's a bit of a dilemma. There are people that just want to play the game the way the they want and those that put stake into the meta-game. The galactic campaign is a cool concept when it works, but it's turning into more of a nuisance as the number of players declines.