Why can't convex lens produce an enlarged image of the moon?

All lenses have a "focal length", or the distance that the lens reproduces the image from the light it collects. By itself, this image is inverted by the lens.

Lets say for this answer, we have a lens that has a focal length of 10 inches. The light passing through the lens is that of an arrow. At 10 inches from the lens, the image of the arrow is formed though it be upside down. The eyepiece of the telescope "magnifies THIS image. As you continue to move beyond the focal point, the image gets larger. Depending on the size of the lens, the amount of light gathered will dissipate and the image will be too dark to see at large size (resolution). So you need a second lens to "magnify the image found at the focal point of the convex lens. So with the one lens by itself you cannot really see the magnification of the lens.

Yes, the lens will produce the complete image of the object. But the intensity of image will be less. This means that the image produced will be less brighter than the normal image which is produced by the lens without any blockage like black paper. I am sure for my answer coz I am an Engineering student.

Convex lenses only produce larger images when the object is placed closer than the focal point of the lens.

Because the focus point is less than 384,000 km away, much less.