Fibre based color paper is subject to higher stain levels due to the process chemistry and so the dmin is not as nice. Also, the light stability is better on RC due to the TiO2 in the support. It absorbs some of the back reflected UV. In addition, RC is less permeable to oxygen than FB.

It all adds up to RC being better for color.

Oh, and you can make a high gloss on RC without the need of ferrotyping, and it is easier to make many different textured surfaces which is no longer important, but once was. They were different than those made on FB.

Drying is quicker and washes can be shorter and replenishment rates of costly color chemistry can be lower.

You see, there are many many reasons.

FB was never used for Ilfo/Cibachromes. The very acidic dye bleach process destroys FB paper.