In simple terms because it engages with the real world and its origins, interactions and change, not (or not merely) with abstractions.

The first chapter of Bertrand Russell’s The Problems of Philosophy (1912, and still used as an introduction to philosophy) titled Appearance and Reality asks whether the table that we sit at corresponds to what we experience with our senses. It concludes: “Doubt suggests that perhaps there is no table at all.”

The book’s final sentence reads: “Philosophy is to be studied, not for the sake of any definite answers to its questions, since no definite answers can, as a rule, be known to be true, but rather for the sake of the questions themselves.”