Switching costs are non-trivial but I would also keep in mind just how valuable “we don’t raise prices” is to AWS for getting businesses to adopt them. In practice that means they don’t lower prices as quickly when the underlying costs decrease but an awful lot of CIOs prefer that to volatility.
When the market is closer to saturation that could change but I think that’s going to hold for at least a decade or two: there is considerably more money being spent on traditional data centers than in the cloud and I’m sure they’re trying to give as few disincentives as possible to those potential customers.
And that doesn’t even get into the technical side of it, which is a logistical nightmare as you mentioned with multicloud. (I don’t even want to think about it for my personal projects!) If C1 has around 50k years of AWS experience among all its tech employees, it will take a long time to match that in Azure or GCP.