An old question but it seems to still be unanswered and I can add my two cents. I think that the OP asks why the bands, or zonal jets, do not all travel in one direction now, after billions of years where a '
An old question but it seems to still be unanswered and I can add my two cents. I think that the OP asks why the bands, or zonal jets, do not all travel in one direction now, after billions of years where a 'dominant' zone traveling in one direction would have time to 'overpower' other zonal winds.
Short answer: There are mechanisms which act continuously on Jupiter's atmosphere, forcing the winds in different bands to rotate in different directions.
Long answer: The reason that they don't form one homologous band is that there are driving forces causing the winds in each band to rotate in opposite directions. The mechanisms which form Jupiter's bands are not certain (as the wiki article explains). One possible cause is something similar to Hadley cells on Earth. On Earth we have similar bands of wind to Jupiter we just can't see them as clearly. On the Earth, these bands are formed due to uneven solar heating over the Earth's surface, which causes the air to rise and fall, and the rotation of the Earth which sets the direction of the wind in each band due to the Coriolis effect. The same mechanisms may form the bands on Jupiter although internal heating could also play a part.
There are other theories - such as the effect of tidal forces imparted by Jupiter's many moons on its atmosphere - but whatever the cause the fact is that these mechanisms act continuously on Jupiter's atmosphere forcing the bands to rotate in different directions.