This.

What I don't think you are allowing for is different choices by different cabin crew.

I think your second crew member (who asked everyone directly) was just more keen to interact with people, and perhaps more keen to sell.

The other crew member, I bet they were scanning for all passengers but only asking periodically as they moved though the cabin - so people knew what they were doing at the time (so they could make contact if they wanted). IF they don't say anything, people might not know they were ready to sell at that point. If they ask everyone it could be annoying - and might slow down the overall service though the cabin.

I'd personally agree with previous posters - if people want to buy something they can signal. I much prefer that to a direct asking of each person - as long as the crew are alert to anyone taking an interest. (and they are often far more alert than you would think).