What is the primary reason the stars of Orion’s Belt appear aligned in a straight line?

Answer

It is purely an effect of our line of sight from Earth (a perspective trick).

The perceived straight line is an illusion created by the viewer's perspective from Earth; in three-dimensional space, the stars are vast distances apart.

What is the primary reason the stars of Orion’s Belt appear aligned in a straight line?
astronomyKingconstellationbeltOrion