Why did the Umayyads move their capital?

Answer 1Damascus was at border of western countries and many worldly enjoys and sins like wine and sex,... were easy and ready for Kings. but in an Islamic society it was difficult. there was the place of living Christian people and wine was not restricted. Yazid the Umayyad King has a poem: if the wine is prohibited so drink it in Christianity religion. he has pool of wine.

Answer 2

The Umayyads had previously been the governors of Damascus and could expect a strong power base if they remained there. Medina was isolated and would have reacted with contempt that the man who overthrew a Rightly-Guided Caliph ('Ali) would have the gall to rule from Mohammed's city. It was primarily a political decision.
muawiya, the governor of Syria wanted to move the capital to Damascus where he was from. This gave him more power