This I totally believe.
Even if the glass of Coke costs 0,1 € and the cookies another 0,1 €, once you factor in the hourly cost of FA during service and all externalities required by catering, 1 €/pax doesn't even seem so high.

Thing is, AFKL won't even shave 0,2€ out of this euro when switching to partial BoB.
Because the FA will still spend time handing out those free drinks. Even if catering is streamlined, most costs don't vary much when you stock 5 drinks instead of 10.

A back of the envelope calculation indicates savings will be minimal if measurable at all. They must be expecting BoB to actually bring revenue... or they are playing another game we are missing completely.