The transfer ban lasts until summer 2020. Chelsea is still competing on 4 fronts (League, UCL, League Cup and FA Cup). As the season progresses Chelsea will have to rotate their players so he'll definitely get his opportunities. It takes some players a little bit of time to get adjusted. And it's not like he's been playing poorly like when Bakayoko came to Chelsea. It's just that other players are playing better than him, and when you look at who's ahead of him, it makes sense to a degree.
Mount was under Lamps last season at Derby and is already familiar with English ball. Willian and Pedro are seasoned veterans. CHO was already getting minutes last year and has more playing time with Chelsea than Pulisic.