The switching costs of changing LLM providers is as low as it gets. All the individuals and startups I know try different models all of the time, even down to the level of choosing which provider to use based on the task. Bigger companies move slower but only because they have lawyers and teams negotiating contracts, not because there is a technical reason that it's hard to switch.
Companies have dealt with supply chain unpredictability by having multiple providers and switching between them since forever. It's infinitely easier to switch LLM providers than it is to deal with physical supply chain uncertainty.