One big reason I can think of is to avoid vendor lock-in. This is why most enterprises use a multi-cloud setup, despite the increased complexity.

If you're only using the frontier providers, it's nearly trivial to support switching between the 2-3 of them that exist without using OpenRouter.

If you are ALSO routing to open-weights models on OpenRouter, then sure. But what we've come back to is that almost everyone using OpenRouter is someone who wants to use open-weights models, and some of them also want to use closed models, so of course open models take all the top spots.

Most enterprises are multi-cloud in that they have multiple direct contracts with different cloud providers.

>This is why most enterprises use a multi-cloud setup

Going to have to say citation needed on this, if you're suggesting most enterprises have infra-as-code that would allow them to switch their entire infra between vendors within a month.