What i mean to say was that when it was felt that existing 2G TDMA/FDMA air interface is not capable to support 3G data rates a need for different air interface standard was felt.
They could have choosen CDMA 2000 instead of going for WCDMA.
As going with former you need only 1.25 Mhz of BW whereas in case of latter you need 5Mhz spectrum,
Spectrum is a limited resource.
regards