While Moving your city would be popular with players, it would be an extraordinarily difficult task for the programmers (like having to ensure it ends up in the same boost-position), and unless it was extremely limited (At the very least, having to abandon all your goods and supplies and not doing it very often) it could very easily lead to server economic imbalances and cheating, like creating cities just to accumulate goods to trade away at a preferential rate to your main city.