I've never heard of it being a requirement but normally PhD students attend them, as a way of networking, finding out about new research in your area or simply a break away from their own work.
Personally I think they are great and have been to quite a few, ranging from small to large.
If you only have a few months before you leave the country, then it would seem silly to attend a conference just so you have done so, rather than wanting to/needing to.