As part of our cabin supervision (checking that there's no rubbish in the aisles, nobody sleeping on the floor, toilets are re-stocked etc.) there is a requirement to do a walk around of the aircraft every 30 minutes. If we're out in the cabin on a service, this is included within being present in the cabin every 30 minutes. There isn't a requirement during this cabin supervision to take out a tray of drinks, although as we do juice rounds in World Traveller, most proactive crew will take out a small blue tray with some water and juice out into Club as well.

It's a very fine line to balance between being "present" and being intrusive, especially on night flights. We could walk through on the dot every 30 minutes, but if you've been asleep you'd have never told. Similarly, most customers don't want to hear crew chatting in the cabin with customers or walking about every few minutes on a night flight. If you're trapped in your seat, it's not rude to press the call bell at all, but with the Club kitchen and so many people wanting different things from their crew, it's very difficult to strike a balance.

I must say I find the OP's description of the crew's smiles to be a bit much as well ... they smiled ... surely that's better than a blank expression or a scowl? Some people aren't naturally smiley, I guess.