What makes you say it is a bad business decision? It seems to be a fine decision to make for things like AWS, since when it goes down, a ton of websites go down and no one blames the site.
There is no way to know whether it is a good or bad business decision just because they can go down when a third party goes down. For example, if you save $50 million a year by firing half your employees and replacing them with AI, but you lose $10 million a year because your site goes down when Claude goes down, then you made a great business decision.
On the other hand a competitor site that is up (or bricks and mortar competitors) might get a lot of business when AWS goes down. If you depend on AWS for operations it might be a lot more expensive than that.
Mostly I think its that management does not blame the person who picks AWS. Its another iteration of "no one got fired for buying IBM/Microsoft".
It is also an issue at other levels: if all a county's businesses rely on AWS (let alone its government) then that gives the US huge leverage over you (sanctions would shut down your economy).
hundreds (thousands?) of companies who based their business on capabilities built around someone else's API. Companies that had important features stop working because a company's API terms and conditions changed. Were you not around for this?
Oddly, I do not think you are wrong. In a pure money calculus exercise, this seems like a no brainer. Naturally, the math gets iffy the moment we are trying to capture something less tangible like 'customer may get sufficiently annoyed to drop us altogether' or 'we are no longer a respected company' or what MBAs would call 'unexpected goodwill extraction'.
I honestly don't care nearly as much as I used to, because I used to be more upset over this. Now, I simply wait to see how much is enough to rile up average Joe and Jenna.