It's easy to get mad about this, everyone would prefer the fancy ceiling. But a lot of old plaster work like this was cheaply and hastily made, a lot of what survives is in bad shape. There may have been good reason to add a barrier between the plaster and the people below. This may even have been the best choice for preserving the plaster until an owner with greater resources could restore it.
This picture invites you to tell yourself a story about what happened, but it doesn't give you enough information to know what happened.