Aside from the geographical convenience, state of art facilities and other advantages that Singapore has to offer, there are two special reasons why top-notch arbitrators come to Singapore: 

1. Non-residents of Singapore entering the country to provide arbitration or mediation services do not need to apply for a work permit and can instead obtain a social visit pass, valid for 60 days. The exemption applies to arbitrators, mediators, legal counsel and other professional advisors (such as translators and transcribers) and applies so long as the case is not religious, racial or political in nature. The social visit pass does not have to be applied for in advance and can be obtained at the point of entry into Singapore.
2. Income derived by a non-resident arbitrator for arbitration work carried out in Singapore is exempt from tax. The tax exemption is applicable to all non-resident arbitrators who are appointed for any arbitration which is governed by the Arbitration Act or the International Arbitration Act or would have been governed by either of those Acts had the place of arbitration been in Singapore.

More information regarding these exemptions can be found here: http://www.mom.gov.sg/foreign-manpower/passes-visas/workpass-exempt-activities/before-notification/Pages/default.aspx#Arbitration-MS

and here: http://www.iras.gov.sg/irasHome/page04.aspx?id=574