This is nonsense. Fiber cables are always capable of the same speed in both directions at once. The actual reason is so they can sell you an overpriced "business" plan if you need upload speeds from the current decade.
ISPs that evolved from cable companies might still be using cable hubs with a common collision domain, but only a relatively small number of subscribers will be riding the same copper — it’s just cheaper these days to convert the signal to fiber as early in the signal path as possible. Plastic wires are cheaper than metal wires, and you need fewer of them (and so fewer switches.)