I'm guessing they want to avoid characters being removed by systems in the stack between the one generating the object and the one transferring bits over networ

I'm guessing they want to avoid characters being removed by systems in the stack between the one generating the object and the one transferring bits over network. Could be more robust if everything (response and p) is re-forwarded through API Gateway or any API Orchestration logic. As you pointed out, whitespace probably is technically superior, adding a useless field might be more convenient in their current stack and can help clients securing their own systems.