"Don't they have any common sense? Can't they see the world is changing?" The common sense and change, unfortunately, are in the eye of the beholder. One party sees change as necessary, inevitable and as the road to prosperity. The other sees it as loss of jobs, increase in poverty and mounting social tension. Of course, a government can bypass the Left, ignore its protests. However, when the Left is, in a sense, the government, it would be silly to expect them to support programmes and policies which negatively affect their constituency. However misguided, the communists are fully justified in protecting and promoting the interests of those who vote for them.
Doubtless, there are double standards and contradictions—one rule for Calcutta, another for Delhi—but which political party is not guilty of hypocrisy? Coalitions work on the carrot-and-stick principle. You give some, you take some. This is not the ideal way to govern, nor does it allow change to be ushered in rapidly. It's messy, slow and unlikely to please McKinsey & Co. By contrast, change brought about through consultation and consensus will be both sustainable and equitable.
I am not a Marxist or anti-globalisation, but when I read very intelligent people deploying very intelligent opinions lambasting the Left, I always find the communist perspective missing from the discussion. For the foreseeable future, the Left in India will remain a potent force. For me, despite the blinkers, their inestimable value lies in their capacity to constantly remind our smug, over-consuming middle class that 'shining' India is a joke for 400 million marginalised citizens.