I do not regularly use either, but my impression is that Cursor's users have primarily been using Claude and are largely switching to Gemini, while Windsurf has a lot of existing enterprise contracts that wouldn't even notice an underlying model switch from the proprietary Codeium model to o3 mini or whatever.

Windsurf users are mostly using Claude too.

Could be that they're negotiating with both in an attempt to create better price leverage. That's what I would do.