There are several reasons for this. When a car advertises a maximum charging rate of 50 kW, that doesn’t mean it can consistently charge at that rate.
When a vehicle connects to a charger, a conversation takes place between the charger and the vehicle — and it’s dominated by the vehicle. The charger tells the vehicle both the voltage and current rates it can accept, and the charger provides only what the vehicle can accommodate. As a result, the vehicle manages its battery to provide the longest useful life by not overcharging it. Here are some examples of things that affect your charging speed: