I don't know why they even bother with all singing groups as a genre anyway. They're not common.
If the public wanted lots of them then the charts would be full of them. But they're not.
Because if you look in the real world the majority of groups who are successful are 'bands'. They are a group who play instruments.
The public don't seem to want a lot of singing groups in general. The public limit them to only wanting 1 or 2 at a time. If there are no other big singing groups around then maybe you have a chance.
But the music scene isn't dominated by Boyzones and Westlifes, or Girls Alouds and Pussycat Dolls, they only seem to have room for 1 or 2 successful singing groups around at the same time.
At the moment as far as girl bands go, you've got Girls Aloud, Sugababes, and are Pussycat Dolls still around?
Then you've got The Saturdays as backup. If the public wanted more girl bands then they would go for them and the charts would have more of them around. But it appears that the girl band quota is full up now and I don't see space for another girl band coming along unless a couple of the existing ones split up.
Westlife slowing down or appear to be splitting (I don't even know if they are still around or not)? Then JLS have the opportunity to slip in there and replace them as a premier boy band. Which is how it seems to be working out.
But another JLS type boy band breaking through? Forget it. It's full up now, The public have got their 1 or 2 male singing groups, Take That are still knocking around, and now the door has closed again. You're pushing it if you expect the public to take on another one.
The vast majority of groups who successfully navigate the music charts play music and have a lead singer.