The moon looks bigger because it’s an optical illusion based on the fact that you see the moon close to, yet clearly behind, familiar large objects like mountains and buildings.
When the moon is high in the sky, the brain “sees” it as a smaller object not that far overhead, no matter what we logically know.
When the moon is near the horizon, its proximity to large distant objects gives a comparison scale and makes us see it as being much larger, although our brain still cannot fully fathom how large and distant it really is.
Some scientists used to believe that the moon looked bigger at the horizon because light beams were being distorted by the Earth’s atmosphere.
However, that theory can easily be ruled out.
If you use your thumb or a coin held at arm’s length to “measure” the moon, you’ll find that it’s exactly the same size no matter where it is in the sky.