Given the prevalence of Opencode and its ability to use any model and provider I don't see reason why would anyone bother with random vendors half-assed tools.

For starters, money. There is no better value out there that I'm aware of than Claude Code Max. Claude Code also just works way better than Opencode, in my experience. Though I know there are those that have experienced the exact opposite.

Are you calling OpenAI a random vendor?

That's like calling Coca Cola a random beverage vendor