I think that people haven't yet really got out of the mindset where you couldn't bring your own food on planes. Now that you can, their providing food (or not) is much less of an issue, but it's still hard, for me, at least, to resist the frisson of thinking "free food!" (even if, as you say, I have already more than paid for it).

No, it's not a deal breaker, but it's something small that makes the customer feel valued/appreciated and not like a walking dollar sign whose presence is an annoyance to the flight crew.

And in an industry characterized by extremely low margins a $0.50 bag of peanuts per person is definitely significant money out of their pocket.

On Ryanair it would be.

The cheapest fare advertised on their homepage is £7.99, London Stansted to Strasbourg (15 August, debit card payment, carry-on luggage only).

A bag of nuts, according to the menu in their FAQ section, is €2.

Its value is a lot more than 50 cents when you've been hauling a baby through airports, sat on the tarmac because of weather, and didn't have time to grab a scrap of food yourself.

You should go look into how Ryanair works. They sell cheap tickets, and then nickel and dime you on everything else.