And more than that it’s about feeling valued and respected. It can be really upsetting when something you’ve gotten used to is taken from you. Especially when you know the cost to the company is just a tiny fraction of the overall operating budget, and unlikely to make any significant difference to the bottom line.
Interestingly at my first job that I worked at, sodas weren’t free, and it never really bothered me. But if they had been free, and one day stopped being free, that would annoy me. I think there is an asymmetry between the satisfaction people get when they use a perk, and they dissatisfaction they get if you take it away.
I've seen it happen. No soda, no food. But the executive assistant will do a lunch run every day for executives. And will pick up drinks too. Or there's usually a stocked fridge for executives near their wings of the building.
Additionally, the service has a value in time and money saved. There are bound to be employees for which it tips the decision to leave sooner. When many different conveniences are cut, more employees cross that threshold.
Finally, there’s a meta aspect to this. If you know a decision is harmful to the company and you see your managers making the harmful decision, it can be harder to keep working for them.
It probably wasn't just the sodas, it was probably a culmination of a lot of changes, and the sodas were the straw that broke the camel's back.
Additionally if the company saves money on such a small scale it sends the signal things are BAD.