One reason is it brings us face to face with a few historical facts that most of us Indians have forgotten. Like what life may have been under British rule, how few people sold their citizens to enjoy the riches and some chose to fight against all odds when compromise was an easy way out. The personal price paid by these zealots was immense - the least we can do is try to listen to their story.
I am not a fan of period dramas and the film could have avoided about 15 mins of reels particularly in first half by shortening / removing certain parts - lion kill (shorten), child birth (remove), king coughing before dying ( shorten) , post milk drinking song - remove etc.
Great way to end the story. Movie makes up for any of the above flaws through excellent sets, great costumes and honest dialogue delivery . Great movie.