And another way to look at it is, because there's no regulation of prices in the US, drug manufacturers can be as greedy as they can get away with.
The Canadian government doesn't negotiate prices, but the arm's-length federal Patented Medicine Prices Review Board is mandated to regulate price increases, but not prices per se. It ensures that price increases are in line with the Consumer Price Index, and that the price of a particular drug is never the highest in the world. And while the review board can't dictate the initial selling price of a drug, it is required to ensure that the price of a new drug is in line with the price of existing drugs used to treat the same condition. Which is why the new Fiasp came on the market at roughly the same price as existing fast-acting insulins.
Each province and territory administers its own public health plan, and many if not most provinces negotiate a maximum price with manufacturers and/or get volume discounts for bulk purchases as a condition for that drug to be listed on the provincial drug formulary (and therefore covered by the public health plan). That helps to keep prices reasonable. It would be nice if that thinking extended beyond drugs, and then an Omnipod PDM in Canada wouldn't cost about 950% (not a typo) more than it does south of the border.
There is no regulation of the prices of generic drugs, and that's where you see the greed. In the press recently was a common generic antibiotic whose price had shot up 1800% (not a typo either) in a couple of years.
I would like to think that even if Lilly didn't make much profit selling insulin in Canada, they would sell it here anyway, just because, you know, the very loud backlash when you deny a life-saving drug to hundreds of thousands of people isn't so great for your stock price.