Explorer pHAT Limit of H-Bridge

Hi, according to the description of the Explorer pHAT, the H-Bridge channels are limited to 200 mA. The datasheet of the DRV8833 gives a limit of 1.5 A or 0.7 A for the DRV8833C. What is the reason for the narrower Limitation of the Explorer pHAT? I want to drive a stepper motor which requires about 300 mA.