What are the reasons behind NIT Delhi being the worst NIT?

NIT Delhi is definitely not the worst NIT given its excellent planet scenario. However, it's true that NIT Delhi hasn't reached the level of other NITs, and it's because it's in its infancy stage. It still has many obstacles to overcome which it certainly is doing gradually. 

The reason NIT Delhi is ranked poorly is that the major criteria considered by these ranking bodies are faculties research work, placement, campus, and infrastructure and sadly NIT Delhi lacks in all these aspects. It has no permanent campus and the infrastructure is also pathetic. The institute attracts less quality professors and has a low permanent-teacher ratio. All these factors combined affect the ranking of the institute.