I see the pilot (or co-pilot) during at least 50% of the flights I take in the US over two hours in flight time. If you've noticed a FA blocking the aisle to the galley with a drink cart and standing posted at attention watching the passengers attentively, that's why. The cockpit door is rarely open more than 15-30 seconds. If either of the cockpit crew actually leaves the cockpit (say to use the restroom), then a FA must take their place and relock the door. This scenario requires a minimum of two FAs, one to watch the passengers / block the aisle, the other to fill-in in the cockpit.