Film is not just a simple chemical entity. It's a combination of many chemical entities, which are carefully chosen and mixed so that they behave in a certain manner. The law of reciprocity doesn't describe the natural behaviour of each chemical entity, but the behaviour of the mixture, which is specifically and intentionally set by the manufacturer (as far as possible, of course).
What you're saying applies to plain silver halide emulsions, or to wet plates, whose photographic behaviour is set by natural laws. Modern films, on the other hand, are carefully designed to help photographers by fulfilling certain criteria, one of which is the reciprocity law.
The reciprocity law is not simply a description of a natural phenomenon, but rather a condition which film manufacturers struggle to make their films compliant with.
Fuji Across is proof that it is possible to comply with the reciprocity law to a much greater extent than most other films do. So, I'd say that the other films fail, because they don't comply with the law as closely as they could.
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