Because R&D is an open process. You never know if and when you will have success. There is no guarantee, and film production is extremely difficult.
It is simply honest and trustworthy to be silent until something substantial can be said.
Acros had to be discontinued because some raw materials were not available anymore.
Certainly Fujifilm started R&D on Acros II before the discontuniation announcement. But at that time it was uncertain whether they will be succesful with Acros II in a short time period. And they don't wanted to create high hopes for something which can fail. Then the dissappointment would have been even much higher in the case of failure.
Cheers, Jan