By contrast, Wifi bandwidth, Internet access, electricity, and so on, are limited resources which someone has to pay for. If the Reader connected their Kindle to their neighbour's power supply then they are unambigously stealing electricity. Viewed in this way, an employer requiring their employee to consume electricity, potentially deprive other users of their home Internet of wifi bandwidth, and so on, is quite clearly imposing an extra cost on their WFH employees which they are not imposing on their office workers.
This doesn't seem ambiguous to me, it's just not become an issue yet because the harm is relatively small.