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.