Bengal's descent into the current situation is a long story, really. It started with the previous CPI(M) government. They did their best to destroy political opposition by building a mass cadre-based machinery, and in the process, destroyed the state machinery. All institutions except maybe the higher judiciary stand compromised.
Mamata has followed the same blueprint and in fact has taken it a notch further. The violence in politics that is the hallmark of the state is a Communist legacy, but she has institutionalized it at the local level. Every residential area has its youth club, which is a euphemism for a bunch of unemployed youth who do her party's budding in return for a monthly allowance.
The CPM destroyed the states economic vitality. An entire generation of youth has grown up without any hole if finding meaningful work, and it is no surprise that their energies are misdirected in this manner.