Figure 2 of the MAX1722x datasheet states only the MAX17221/3/5 can be driven by a push-pull GPIO, implying that it cannot be done by the MAX17220 or MAX17222. That is not entirely true; the MAX17220 and MAX17222 can be driven by a push-pull GPIO, but there is an internal 100 kohm pull-up resistor between EN and OUT, which gets activated after EN is above its logic High threshold. The push-pull GPIO must be strong enough to pull down EN, when the internal 100kohm pull-up is pulling EN to OUT. Also, you would need to account for the excess leakage current which will be created due to the current path between OUT -> internal 100kohm pull-up -> EN -> GPIO. The advantage of using MAX17221/3/5 with GPIO to drive EN is that you don't have to worry about sizing the GPIO to fight against the internal 100kohm , and the excess leakage current associated with the internal pull-up.