a phrase used to ask for the reason or explanation of something

इसका कारण क्या है

English Usage: How come you didn't call me yesterday?

Hindi Usage: तुमने कल मुझे फोन क्यों नहीं किया?

introduces a clause that presents a reason or justification

यह एक कारण या स्पष्टीकरण प्रस्तुत करता है

English Usage: How come they are leaving so early?

Hindi Usage: वे इतनी जल्दी क्यों जा रहे हैं?