I think this makes a lot of sense - that way people that want to bring their own food don't feel ripped off.

Payroll tax. And cutting perks is easier than cutting salaries.

Perks have the advantage of being pre-tax.

So if you get $10 worth of perk (assuming it's something you'd buy anyway), it only actually costs you somewhere between $5-8 depending on your tax bracket.

Why? That is, is there some specific social good that the authors of the tax code were intending to accomplish by allowing companies to pay for lunch for their employees pre-tax, or is this an unintended consequence ("loophole") of some other coherent goal?

It seems to me like there isn't any reason for a tax code to allow not paying taxes if the company is calling a transfer of money to the employee for the purpose of buying food as a "perk", and yet tax the same money if it's called a "salary".

Nothing that high minded. You are simply taxed on income. Money the company spends isn't personal income.

But that interpretation has ridiculously easy loopholes - why not just reduce my salary by $10K and give me a $10K company-managed Amazon budget for personal expenses? Why not just let the company book my personal vacation travel via payroll deduction? Why not have the company rent my apartment and sublet it to me? etc.

I'm coming at this from the position that the law must say, if you're giving a person access to a cash spending account that lets them buy things for themselves but not giving them the cash directly, that still counts as income. Is that true? If it's not true, why isn't everyone taking advantage of the loophole? If it is, why is lunch a special case?

Only some of the benefits are excluded from income, food and health insurance being the most popular. The rest have their value added to income and taxed accordingly.

So why doesn't every employer give me a food FSA or something? Pretty much everyone spends some of their salary on food....

Plus if they just pay you more, you can bring a packed lunch to work and save the money towards holidays / savings / gifts / financial independence / whatever.