The solid body electric guitar, the Dinosaur mainstay of the instrument world, is not an instrument that can stand alone. It needs a separate device to amplify its voice. In fact, it needs this second device to produce any type of tone associated with the Dino sound. And while electric guitars create many styles of music, some only require the clean reproduction of the picked notes. In those cases, any amplifier of appropriate loudness will suffice.
The heavy rock and metal voicing requires a more specialized amplifier that does far more than just amplify what you've played. It must add ingredients to the voicing. It must be responsive to different techniques the guitarist uses. When a Dino electric guitarist plays his instrument, he's not playing the guitar through the amp. He's playing both his guitar and his amp. So when it comes to the voice you want your guitar to sing with, many Dino guitarists consider the amp, the most important contributer to the sound.