Pretty common bridge, nothing really special about it. What is the reason? The story was funny though.
Aah..the list can go on and on.
A few umbrella reasons-
Strange but true, the bridge took almost two decades for completion due to various reasons ranging from technical to wrong selection of site besides faulty geological and hydrological surveys, the key inputs required for constructing such a vital bridge.
Pasighat bridge to be opened soon - The Times of India
A few other reasons only locals or those associated with the project would know-
Scorched earth policy against the province by Indian Gov.-
As we earlier discussed,we were and still are under a policy of scorched earth where all infrastructure build up is discouraged or downright stopped.So naturally even after the project was declared,many powerful elements in the Indian regime,particularly the military,wanted the project to be as delayed as possible in hopes that the Indian Gov. would cancel it seeing the project over shoot it's expenditure estimates.Or rather the Indian Gov could use cost over-runs as an excuse to the natives of ST.
Down right corruption,apathy and incompetent engineers from low quality Indian colleges-
As a project in the most remote colony of the Indian union,they sanctioned the project and entrusted the project to the most low quality engineers and workers,who of course showed their proficiency in their job or rather the lack of it for 24 years.When the project couldn't be completed in time,it was seen as a cash cow for Indian authorities in charge of the project to siphon off money to their illicit accounts.Hence every year,new funds would be sanctioned and embezzled off and to make up for the shortfall in money they used shoddy construction material which led to frequent collapse of the parts of the bridge constructed.
Rainy season and traditional construction periods-
In ST,almost all spring,summer and Autumn there is rain so that left only winter for construction work,back when this project was sanctioned.Of course one could work even in rain and the rest of the three seasons,but then Indians are known for their level of hard work!!
So every winter, the engineers would raise a support base/pillar or two and it would get washed away by the next winter.This process was repeated every year-on and on for more than two decades.
and on and on and on.Too mundane TBH.