Well, if they're spending millions on it in general then many employees taking 1 or 2 home every day is actually probably a much greater financial 'burden' on them than a handful of employees taking entire flats every now and then.
And you also don't tend to put up signs like that unless your goal is to change everyone's behaviour.
Yes, "you" do. You specificaly may not do that, probably most people around here will not do that, but lots and lots of people do, enough so that most signs are put down by this kind of people.
It is kind of staggering to think of 90,000 employees times 2 sodas every workday.
Those 90,000 employees cost about $45M a day to employ, $35k on drinks is meaningless. Especially against the PR disaster of a thread full of potential employees hearing you hide the soda at night.
But, as someone said, if someone is stealing from you and views it that way you should deal with them personally, directly, and immediately. Passive-aggressively hiding soda is only going to make them switch to office supplies, if you're lucky.
Really, this attitude is precisely the problem. You're looking at this as a confrontation from the start. Perks like this only work if they're offered and accepted in good faith. If you don't trust your employer to interpret your soda consumption charitably, your employer is getting no benefit from offering it.
Basically, if you want your employer to offer snacks and soda, be grateful about it and don't look for trouble.