Except they do sell aluminum packaging and, having worked in the beverage industry, it most definitely factors into cost of goods sold calculations. I worked in bottled water when a bunch of different New England states decided to adopt different deposit laws for bottled water, which caused the kind of production planning nightmare I like to solve. All of a sudden we had to figure out which state with which deposit laws our product was destined for, and ensure that the correct labels were applied at time of production. Easier said than done in a world of large-scale regional product distribution and production runs on massive scales.
Regardless, there was no level of production or financial planning that assumed those deposits were anything other than packaging expenses that I was aware of. Money that came back was tracked, but not planned on as a reliable stream of funds.
The only laws I know of governing can deposits involve interstate transfer of empties. For instance, I would be committing a crime if I took my embarrassingly large pile of quarantine empties to Michigan, where I could attempt to redeem a $0.10 per can deposit. There have, in fact, been sting operations and arrests made for this type of activity. Great news articles when it happens.
I suppose that brings me to the ethical considerations I didn’t even ponder until you had to rain on my brilliant plan. Even if it is technically legal, it may not be a good faith business transaction to acquire a keg in the fun and rewarding way I’ve described.
Putting my BA hat on, I could imagine brewers managing kegs as assets, not as sunk cost packaging materials. That would make a lot more sense if they do, indeed, cost upwards of $100 to manufacture.