Am I supposed to keep switching alliances in order to artificially keep the game going?
Not really. If you want to go solo for max points for the lulz you'll have to throw in a off-faction quest step or 2 to throttle advancement of "your" faction a bit to so you can reach a final quest stage that allows you to "overshoot" the end of the track by several points in one go for high points from multiple stacked agendas for that faction. But that's a bit ridiculous.
If I pledge allegiance to one faction then the game feels like they won and I'm just helping them move their agendas forward.
As long as *your* agendas are in the bag too who cares what the factions think, they're just NPCs.