Primarily because they are genetically inferior when it comes to most athletic or sport endeavors. And India's infrastructure is only a small factor as to why Indian athletes don't perform well, as there are other countries with just as worse conditions infrastructure with athletes who have routinely won Olympic medals (past & present). In fact in the 24 Olympic games India has competed in, they currently have just 26 total medals.
Solid insight, don't they worship cows instead of eat them?

