Uh... because it's probably the most beautiful building ever erected?
"Personally I never quite understood the hype around Taj Mahal. Its an Islamic monument built by a muslim king. Why do Indians care about it so much ?"
....because it is not an "Islamic monument" but a Hindu Temple occupied/appropriated by Muslims. I am surprised you dont know.
Tajmahal: The True Story:
http://www.stephen-knapp.com/true_story_of_the_taj_mahal.htm
http://www.hindunet.org/hindu_history/modern/taj_oak.html
http://www.hindunet.org/dynamic/modules.php?name=Content&pa=showpage&pid=92&page=3
It might have been sanctioned to be built by a Mughal emperor. It was built by Indian laborours, many Hindu. It was designed by Indian, Turkish and French architects.
Seriously, do you really not find this building beautiful? You have to be there to be stunned by its size, scale and beauty.
Even if you dont like the people who built it, the building is still beautiful, and fascinating from a historical perspective.
In Spain they still like the Alhambra and alcazars, even though the Muslims built those.
They are part of history, and should be cherished as such. You should like the Taj Mahal because it is part of history, and a great building aesthetically and architecturally.
The Taj Mahal, in my opinion, is one of three things that lives up to its hype. The Grand Canyon and Beethoven's Ninth Symphony are the other two.