Why is the sunlight bright?
It (the sun) produces a lot of light.
If you mean looking at the Sun, it's bright because it is like a giant flashlight that produces tons of light.
If you mean why is the sky not black (because wouldn't the sunlight go straight through the air?), then the reason is because some of the sunlight is NOT going straight through the sky. Some is reflected all around, so the sky looks like it's bright, because it was "given" light by the main source - the Sun.