You're attributing gatekeeping to the wrong place here. The customer is the gate and the customer's unavailability is keeping the gate shut.
The PO reduces that inadvertent gatekeeping by being always available with customer insights so the devs don't twiddle their thumbs or worse, build thr wrong thing, because they were guessing what the customer wanted in the absence of actually talking to them.
The PO reduces gatekeeping because they are an always available customer.
