Why tiger has 9 subspecies not 1?

[tigerluver]

Hi @P.T.Sondaica,
The tiger subspecies issues is not agreed upon by everyone just yet. More recent studies have called for 2 subspecies, the island tigers and mainland tigers. Simply put, the bases of these studies is that there is not enough genetic difference between the mainland subspecies to warrant the label.

On the other hand (such as this one), older studies feel this difference is enough. Unlike the term "species", the term "subspecies" has not yet been given a unanimously accepted definition. For instance, orcas have ecotypes rather than subspecies. The difference? Depends on who you ask. 

Another reason why the authors such as Cooper and Kitchener propose a 2 subspecies classification is, from their own words, to have a "pragmatic approach." Meaning, time is running out and populations of the "subspecies" are running thin and thus, being too specific with subspecies is unneeded trouble. Here, scientific definition is being given in context of reality. Here's a short article that discusses the pros and cons of the 2 subspecies vs. multi-subspecies debate. Reply