FUNimation lost Saban Entertainment's partnership circa 1997-ish, meaning they didn't have a network (like FOX KiRAB, for example) to use so they also lost money. When CN picked up an order for more episodes (i.e. edited episodes 54+) FUNimation didn't have the money to use Ocean and probably wanted to start up their own in-house production (meaning a studio down in Texas where they could make use of its pool of actors and save money). Without Saban FUNimation also couldn't hire Shuki Levy, and thus instead of using the actual score by Shunsuke Kikuchi they hired Bruce Faulconer and his boys at Cake Mix Productions to score the series from [edited episodes] 54-276.
FUNimation made the right choice, I feel. If they hadn't done what they did we wouldn't have some of the best dubs in Anime right now (barring their Dragonball stuff, which is horribly inconsistent and poorly written).
It should be noted, however, that the Ocean Group did dub more Dragonball Z for and International airing. This dub ran from [edited episodes] 108-276, covering the last bits of the Trunks episodes all of the way through to the end of the series. Peter Kelamis voice Gok