What factor limits the extent of the observable universe, creating a cosmic horizon?

Because the universe has a finite age, light from objects too distant has not had enough time to reach us.

The observable universe is defined by how far light has been able to travel since the universe began its expansion. Since the universe has a finite age, approximately 13.8 billion years, light emitted from galaxies beyond a certain distance simply has not had sufficient time to cross the vast expanse to reach Earth, regardless of the expansion rate. This boundary marks the cosmic horizon. Even if expansion were not a factor, this finite travel time limits our view. Furthermore, when expansion is included, objects that have receded so quickly that their recession velocity exceeds $c$ are effectively moving out of causal contact, meaning their light will never reach us.