I'll guess this is because the A5000 is designed for the "Oriental" market, and someone at Yamaha has decided that Oriental musicians are more likely to have multiple, or unusual, time signatures within the style than non-Oriental musicians.
In my opinion, music is just music... if one or more genres need some different timing sections, this must be USER's choice on how he/she is writing style. But the function must be there, even if the keyboard is made for Europe, USA, Canada, Africa, Australia or other continents
Since this came (well) after Genos, if we do get a new Genos firmware, I'd expect to see this feature being added. But who knows if that will ever happen ...
I think Yamaha will move this feature for Genos 2, as long as there was this last update of firmware, and PSR-A5000 is launched about half of a year before this last update of Genos. I cannot believe that in this time Yamaha's engineers could not prepared an update of Style Creator for Genos too... It is only a marketing thing, and this affects all users, not only east-europeans or other users which really needs this feature.
I've sent a lot of emails to Yamaha Europe, but nothing happens. I have a lot of friends here in Romania which are Genos users and they also sent mails to Yamaha Europe, mails which are only sent, but nothing happens. We (at least east-european musicians) are not take in care about Yamaha Europe. We talk in vain...
Regards,
Vali