In answering the question in the title it is important to refer to the date of this article because things are changing all the time and getting worse for Bengal tiger conservation. This article is quite short for the simple reason that it is based upon the succinct reasons as stated by the people who assess that the Bengal tiger is endangered, namely, The IUCN Red List of Threatened Species.
The authors of the webpage concerned refer to “range decline” as the main reason for their assessment that the Bengal tiger is endangered. In other words the Bengal tiger occupies less and less space in the part of the world where it lives (see Bengal tiger habitat).
They state that the estimated area occupied by Bengal tigers in 2006 was less than 1,184,911 km² which represents a 41% decline from the area estimated by Dinerstein (and colleagues) in 1997. Interestingly, there appears to be no estimate more recent than 2006. That indicates to me that conservation efforts are neither intense nor effective enough. By contrast the market for tiger parts to feed the Chinese ancient medicine market is as active as ever and more money goes into that market then is ever going to go into conservation.
India suffered the most range contraction. Biologists think that the primary reason why there has been a decline in the area occupied by the Bengal tiger is poaching and habitat loss.
They also state that a decline in the range of the Bengal tiger is a strong indicator of population decline. They also state, surprisingly, that an average of 55% of “Tiger Conservation Landscapes” (priority landscapes for tigers) consist of non-tiger habitat. I read that to mean that over half of the area set out for Bengal tiger conservation is inappropriate for the animal. Because of this they argue that “the declines in population and area of occupancy are greater than the 41% estimated”. It is likely that there has been a 50% or greater reduction.
In addition, they state that over the next three generations, 20 to 30 years, there will be further and similar reductions unless conservation efforts are stepped up.
The root cause then as to why the Bengal tigers endangered is habitat loss and poaching. I hope this helps.
