> just looking at the pics it is impossible to gauge whether it is 400sqft or 900sqft

Those are not good pics. Probably* for the same reason, to hide size and maybe something else.

*Depends on culture and I don't know about NYC. I've seen another landlord's market where quite a few landlords just post one or two useless photos — and even heard advice to pay attention to such postings as they're definitely not prepared by a professional agent.