Here's why:

* Phaneritic textures are characterized by large, easily visible mineral crystals. These crystals form when magma cools slowly deep underground (intrusive setting).

* Extrusive igneous rocks form from lava that erupts onto the Earth's surface. The rapid cooling and solidification of lava doesn't give crystals enough time to grow large.

Other textures common in extrusive igneous rocks include:

* Aphanitic: Fine-grained, crystals too small to see with the naked eye.

* Porphyritic: Large crystals (phenocrysts) embedded in a fine-grained matrix.

* Vesicular: Contains many holes (vesicles) created by gas bubbles trapped during cooling.

Let me know if you'd like more detail on any of these textures!