Because it isn't used by Grab&Go. Time Slot Interval, Max meals per time slot and Max orders per time slot on a location only throttle the time-slot picker shown in the regular meal-prep/à la carte checkout when a customer picks that location as a pickup point (the day-by-day delivery/pickup step of the cart). The Grab&Go ordering flow (/grabandgo) never reads these fields - it only checks the location's Grab&Go Open Days, its Cut-off Timer, and each meal's on-hand stock, with no time-of-day slot or per-slot count limit. If you need to cap how many Grab&Go pickups happen at once, use the on-hand stock quantities (Stock Management / Edit Stock) rather than the time-slot settings.