i'm not saying it will come, but that would be a hilariously bad reason for it not to come.And it won't come. Just because online. Online on PC ( and surely a crossplay) would be full of cheaters. Online built during GT Sport and continuation of that foundation in GT7 on console online racing would be ruined. And surely Kaz wouldn't allow that for sure.
Check what happened with last Forza Motorsport. Full of cheaters