It is not a matter of stepping aside for someone else's convenience which I agree if were the issue would be simple kindness at no cost to yourself.
The issues are twofold. One is one of safety as escalator accidents are increasing with many people walking on them. The other is that riders are encouraged to stand two abreast so that a greater volume of people may be moved at the same time.
True, but I personally feel it's not my place as a foreigner to be the busy body enforcing JR's new rules that from my observation last week, 95% of people are ignoring. I would just feel strange and uncomfortable doing so. With the temperature in Shinagawa Station feeling about 120, I was perfectly happy to stand on the left and move as little as possible.