Do all ISPs ask for old routers to be returned so they can be recycled/ re-used. I notice that BT charge £50 to a customer if they don’t return theirs - what do others do?
Most providers these days will charge for non-return of a router after a period beyond the contract ending.
Part of that cost will be to fulfil what it costs them to provide you the router. They’ll be paying less than that per device, in bulk from an overseas manufacturer.
However, the main reason for the charge is that when they get the routers back, they’re repurposed or refurbed, or recycled, so the charge not only covers their losses, but it acts as an incentive for customers to return them; as many users would just dispose of their old router in the household waste bin. That then ends up in landfill… The harsh heavy metals in the circuitry can be detrimental to wildlife and ecosystems.