The fundamental reason is that the beam emitted by the laser pointer is not a parallel beam, but scattered light distributed in a small cone angle. Considering the characteristics of light propagation along a straight line, it is natural that the farther the distance, the larger the spot.

So why isn't the beam emitted by the laser pointer a parallel beam?

First, because the luminous body of the laser pen is not a point light source, not all the light it emits comes from the focus of the reflective bowl. Even CREE XP-G, an LED with a small core package, can't be ignored when used in flashlights (usually with a reflective bowl with a diameter less than 35mm). For the same reflective bowl, if LEDs with different core areas (such as XP-G and XM-L) are used, the projected spot area will be obviously different.

Secondly, due to the manufacturing and assembly errors of the reflective bowl, there is more or less the problem that its focus does not coincide with the LED center.

Further development, in fact, the laser pointer does not need to pursue such things as the smaller the spot, the better. Many beginners like to pursue long-distance shooting (that is, the flashlight beam has small cone angle, concentrated beam and small spot), but it is precisely because of too much focus, too small field of vision and dazzling spot that it is very uncomfortable to use this laser pen in practice.