In the case of India, we know so little simply because we don't have any written records until relatively late. The reason we know so much about Mesopotamia and Egypt is because there is a vast abundance of written material from those areas, and people have long ago deciphered Egyptian hieroglyphics and Mesopotamian cuneiform (there are over 100,000 cuneiform tablets from the Third Dynasty of Ur alone). In contrast, although the Indus Valley Civilization may have used some kind of writing (or at least symbols), nobody has managed to decipher the IVC script/symbols, so we can't say anything about that civilization beyond what archaeologists tell us. We know absolutely nothing about the political or dynastic history of the Indus Valley Civilization (or indeed, if they even had kings and dynasties like in Egypt and Mesopotamia). It's actually not until the 3rd century BCE that we have physical, concretely-dated written texts from the Indian subcontinent, in the form of Ashoka's edicts. It seems almost certain that the Classical Indian civilization obtained the knowledge of writing from the Middle East during the Achaemenid period, since the word for "writing" or "script" in Sanskrit and other Indian languages is lipi, which is a borrowing from Old Persian dipi, which is itself ultimately derived from Sumerian dub via Elamite and Akkadian. Middle Eastern influence is also apparent in many other Sanskrit words that refer to writing, literature, and administrative work, such as the words divira ("writer, clerk"), pustaka ("book, manuscript"), and mudra ("stamp, print, seal"). However, even after the 3rd century BCE, it is seldom that we find an abundance of Indian inscriptions or texts that can compare to ancient Mesopotamian findings, largely because the wet and humid climate of India is not very conducive to the preservation of palm-leaf manuscripts (the preferred written medium of ancient India).

Moreover, once we do have written sources, they do not include the type of historical texts that were created in ancient Greece and China, like the works of Sima Qian or Herodotus. For whatever reason, ancient Indians did not approach history the same way that the Greeks and Chinese did. There are no chronicles of any Indian dynasty like Ban Gu's Book of Han, no detailed accounts of any Indian war like Thucydides' History of the Peloponnesian War (unless one includes mythological texts like the Mahabharata), and certainly no attempt at a scientific analysis of history like we see later in Ibn Khaldun's Muqaddimah. The closest thing to "history" in the Indian context would be religious texts like the Puranas, which often describe real-world historical events infused with mythology; historical plays like Vishakhadatta's Mudrarakshasa (a drama from the Gupta period that purports to depict Chandragupta Maurya's rise to power); and biographies of notable kings like Banabhatta's Harshacharita, which tells the story of the famous 7th century ruler Harsha. We can still glean a lot of useful information about Indian society, religion, philosophy, etc. from primary texts, but an in-depth and detailed description of ancient India's political history is simply impossible given the types of sources available to us.