I think it's because not enough tickets were sold.

1) "Sadly the tour needs to come to an end by the end of February due to family and personal commitments for Emma, Geri, Mel B, Melanie C and Victoria. It was announced in June that, as well as the Europe and the US, the girls planned to visit Australia, China, South Africa and Argentina. Due to the phenomenal demand for tickets in the UK and the US along with the touring logistics for such a massive production it was not possible to fit everything in. As the girls return to normal family life and the kids go back to school they are reviewing all the options, who knows what the future might bring! The girls said: “We’ve had such an amazing time over the last 3 months. It’s been incredible being back together and seeing our fans again. We want to thank everyone who came to see us. It was all so mad the first time round, so we’ve really been able to appreciate it properly this time. There have been so many highlights and good times that we know it will be hard to be apart after Toronto. Really sorry if we didn’t get to see you this time round. We all have other commitments in our lives now but who knows what will happen next.”" Source: http://www.thespicegirls.com/news/080201announcement 2) "Due to the expansion of the British and North American legs of the tour, it was announced on 1 February that the end of the tour would take place in Toronto, on 26 February 2008. Dates in Asia, South America, Africa and Australia were cancelled due to touring logistics and personal commitments. At the sold out concert at Madison Square Garden on February 18th in front of 12,000 fans it looks like the Show was recorded for a DVD. But no comments were made from the Spice Girls or their Management. There is wide speculation this will happen before the end of 2008, however." Source and further information: http://en.wikipedia.org/wiki/The_Return_of_the_Spice_Girls

i feel ya.i am a super fan and started a spice girls fan club and we got tickets to the show in Australia and our club was soooo pissed that we took charge and protested outside of their tour managers house. lol!