I've always thought the "buy me a cup of coffee" was a thinly veiled euphemism for "give me beer"
edit: also, I have contributed. There's this one android app that works to translate between different wargaming/miniature painting paint brands (as in color matching), the dev straight up asks for a contribution for beer. It was so brutally honest I had to.
Making coffe at home is always cheaper, that why it's attractive to sell coffee, I'm guessing that a coffee place buys their coffe cheaper than you, but they pay rent, staff, other bills and take the risk of owning a business.
And the price of coffe has high correlation with it's availability. No one wants to walk a mile outside of the city center to buy a coffe on their way to work even if it's 80% price difference, and that is what allowed them to sell cheap coffee for higher prices. But there's more to it than that, you have different variants of coffee, some like to pay a lite premium to get a more exclusive one etc etc, there is probably a whole science about coffee pricing.
I wasn't actively aware of this for most of my life until I recently visited a clients office. Buying someone a cup of coffee is an entire thing. There's no free coffee. You have to purchase every single cup. And you first have to walk several minutes to the place where they sell the coffee. It blew my mind. I'm used to drinking one cup after the other without even giving it any thought. Coffee machine right next to me or around the corner. There, coffee incurs friction and cost.
So when you invite someone for a cup of free coffee, this can open doors for you. I'm not kidding. People get all excited when you offer them a coffee break on your dime. And there's levels to it too. There's the regular coffee, and there's the premium one. For the premium you have to walk longer and wait in line until the barista serves you.
It's a key component in office politics when coffee access is regulated.
Why anyone would restrict access to legal stimulants in the office is unclear to me though. Put espresso machines on every desk!
I feel like I'm the only one here eloquent enough to attack this preposterous stance, so allow me to gather my wits to plead my convincing rebuttal when I say:
boooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo! (that was hard to type on a smartphone)