To be fair, there are a number of companies who have made a go at open source routers but ended up deciding on a proprietary path after all—thinking especially

To be fair, there are a number of companies who have made a go at open source routers but ended up deciding on a proprietary path after all—thinking especially here of Ubiquiti's RouterStation line and the Mikrotik RouterBoard. Plus there are a number of options for open source router OSes that you can install on standard PC hardware. I don't know that this proves anything one way or another, but I think it's a bit simplistic to imply that this kind of thing doesn't exist purely because it's never been tried.