Earlier quoted context omitted.
Have you considered checking the actual AWS contract and the limited liability they explicitly stipulate in contracts and even linked docs from marketing materials? If you read the fine print, you'll notice something funny. You are largely responsible for data loss, SLA claims require you to present concrete evidence, and the remediation you accepted is usually credits for future spend on specifically the same produc…
They didn't mention anything about SLAs. This is about all the time, effort, paperwork and risk it takes to add yet another vendor. Having fewer vendors does actually reduce risk, as long as your chosen vendors are reasonably good. Though the bigger reason is certainly avoiding the additional bureaucracy, which is partly self-inflicted in larger companies but also not without merit.
I'm just tired of the 'everyone follows their immediate incentives while the system stays incoherent' as the de facto reality. I think shedding some light over the actual mechanics would maybe make someone consider 'perhaps we shouldn't allow our acquisition team just turn off their brain and choose the default to cover their bottoms; maybe vendors are worth more decision investment via actual thinking instead of performatively ending up on the default choice after a little ritualistic game of "eeny, meeny, miny, AWS"'.
I think it's worth pointing out that Jeff Bezos would fight this tooth and nail from happening in his companies. He popularised 'process as proxy'. Yet AWS as sold to external enterprises is the exact proxy Bezos warned against internally. Do what Bezos does, and even what Bezos preaches, just don't do by default what Bezos sells.