There are 2 possibilities as to why they relocated him that come to mind (could be others, but these seem to be likely):
1: The rest of the herd are all female (they actually are, not speculating), and none of them would mate with him and/or accept him into the herd.
2: They are not wanting any further breeding of elephants at the park.
<<UPDATE>>
Upon reading the actual article here it tells why (basically #1 above, with further reasoning):
Asian Elephant Spike Leaves Busch Gardens Tampa - Touring Central Florida