* Distance: Stars are enormous balls of burning gas, but even the closest star to us (Proxima Centauri) is 4.24 light-years away. That's a distance of over 25 trillion miles!
* Angular Size: Because of their immense distance, the light from stars spreads out over such a vast area that when it reaches us, the angle it covers is extremely small.
* Our Atmosphere: Earth's atmosphere also distorts light, causing it to scatter and twinkle, further contributing to the point-like appearance of stars.
Think of it this way: Imagine a tiny pinhole in a wall. Now imagine shining a flashlight on that pinhole from across a large room. Even though the flashlight beam is quite wide, the light coming through the pinhole will appear as a tiny point of light. The same principle applies to stars, but on an unimaginably larger scale.
Note: While most stars appear as points of light, some of the brightest stars and planets can appear slightly larger. However, even those are still too far away to see any detail beyond a point of light.
