This is intentional.
The way the morale function works is sqrt(30^2+12^2) ≈ 32. Where 30 is the morale from music, 12 is the morale from the chips and 32 is the finale morale bonus.
Morale does not stack linearly to prevent players from easilly stacking it by drinking 10 different kinds of drinks and ect.
Ok, but I get 30 morale from music alone, making food irrelevant. Or in your words sqrt(30^2) = 30. why should one bother crafting enjoyable food when you can just eat roasted rhizomes and smoked fish/meat?
I was under the impression that it was only morale from a single category that had diminishing returns. So +30 from music and +12 from chips should add to +42, but eating a +10 food after that would make the total 30 + Sqrt(12^2 + 10^2). Which makes each source of morale still relevant, but prevents stacking food buffs to ridiculous levels.