Probably just because by the time the 060 came out, Apple had already started introducing the Power Macs.
I understand that apple wanted to kill the 68K line and the 060 would have made the PPC machines look bad.. (because they were), but...
I mean someone like Sonnet, would have been a nice upgrade for the 68K macs and even better because the software and OS were still mostly 68K based and the PPC macs had to do a lot of emulation.
