The explanation is that there is no 'plausible explanation'.
Bihar is THE poorest state in India by many metrics. The way out of poverty and squalor for a majority is getting a good score in the Secondary School leaving exams - or minimum pass the damn exam - where you qualify for state / central recruitment, military, admissions to college and so on.
Just like BRICS, India got BIMARU states - Bihar, Madhya Pradesh, Rajasthan, Uttar Pradesh to signify 'sick' states - BIMARU in Hindi means 'unhealthy condition'. Think of a BIMARU state as Appalachia or Louisana, but more downtrodden and poor.
Here is an anecdote from my uncle - who did his MSc in Physics way back in the late 1980's from Kanpur, a big city in Bihar's neighboring state Uttar Pradesh - another basket case. The college he studied is DAV College, Kanpur, next to the big cricket stadium Green Park.
During the exams students were three types of service by the local strongmen - mostly wannabe politicians, with support from the caste based political parties...the cheapest tier will allow you to copy from your notes during the exams. The middle tier will allow you to write the exam from your hostel room. The topmost tier they will find someone else who is an expert in the subject to write the exam for you.
These wannabe politicians later represent the state and its constituents in the local and central governments. And now you can understand where are how the criminality of the typical North Indian caste based politician comes from....its inbred. Only the toughest and the most criminal will survive.
I am from Kerala - an entirely different world from the BIMARU States. Think of upstate New York or Pennsylvania - but more tropical. The world described above is alien to us...just like its alien to you.