Let's use an imaginary example, to avoid confusion with real team loyalties, beginning with an imaginary sport, SpaceBall, played in zero gravity (in orbit until it becomes possible to cancel out gravity over a small portion of the Earth's surface, at which point the popularity of the sport takes off). Players navigate about a polyhedron-shaped arena using arm-powered flaps (wings), rebounding off trampoline-like walls, and manipulating the ball with their legs, holding it between their knees as they fly, dribbling it with little nudges as they accelerate and repeatedly catch up with it, or shoving or kicking it to pass it to another player or move it nearer to their own goal or attempt a score. Because the wings afford little control at low speed, the usual practice is to take full advantage of the walls to build up speed, so players can be seen flying through the arena in all directions. To add just a bit to the excitement, players have the option of storing part of the effort they exert in the form of compressed air, which can be released as a jet, accelerating them 'upwards' meaning in the direction of their heads. Near collisions happen continuously, and actual collisions resulting in injuries are quite common. Also, although technically forbidden, except to knock the ball from the grasp of the player who has possession of it, players frequently make intentional contact with their opponents, kicking or slapping them with their arms. It being very difficult to distinguish between intentional and accidental contact, only the most obvious instances are penalized.
Because of the huge expense involved in building an arena, there are only a handful, essentially one per continent, and because of the huge investment required to build a competitive team, only the largest metropolises have their own, while most teams are franchises relying upon something other than specific geographical identity, such as a broader cultural identity, to build their fan bases. Monetizable fan bases are critical, so the investors who originally built or who later bought the teams can recoup their money and make a profit.
The appeal to broader cultural identity means that the teams become surrogates for actual inter-cultural tensions, with the outcome of specific contests frequently being portrayed in moral terms and the elation or dejection from a win or loss frequently spilling over into the streets.
Like the teams in this imaginary scenario, political parties have set themselves up as the champions of various cultural segments, usually multiple such segments, in the effort to patch together a plurality of voters. And, even though they may be put off by the others with whom they find themselves lumped together, and by some of the positions taken by their team's candidates, voters usually hold their noses and vote for the team with which they most strongly identify, with a lot of dark money going to insuring that any combinational irritations aren't felt strongly enough to keep them from doing so, and magnifying the irritations that would be experienced by those switching to a different team affiliation.
This nose-holding propensity is what makes it possible for the deep pockets, essentially investors, to bankroll one team or another, in the assurance that victory will result in a more favorable state of (financial) affairs for themselves.
Rather than go on, providing real-world examples, I'm going to cut to the chase, which is that if you would like to help shrink the influence of big money on politics, one way to do it is to participate in MAYDAY.US, the crowd-funded effort to elect "a Congress committed to fundamental reform by 2016."