Chalfontim,
The reason could be anything but the two most common causes of Go Arounds are an aircraft landing ahead that is slow to clear the runway or an 'unstabilised approach'. That last reason sounds a lot more dramatic than it actually is so I'll try to explain.
Like most airlines, Emirates have set strict criteria for their crews to meet in terms of tracking, rate of descent,speed etc. when flying an approach. There are distinctive 'abandon' points which are at 1000' aal ,reducing to 500'aal the if you are visual with the intended runway and/or approach lighting, where you HAVE to be stabilised. If you are outside the parameters you have to discontinue the approach and Go Around. If you 'push it' the company's Flight Safety Department will want to have a 'chat' with you.
Trying to 'stabilise' a 300ton'ish beast from 160kias at 1200' aal to 140kias'ish at 1000' aal (i.e. less than a mile or 2 miles if you use the absolute min. of 500') is 'exciting' enough with a headwind but if there was none or even a tailwind(a la DXB) it can get fairly close. I hope this helps.
