Silmarillion - Chapter 13 - Of the Return of the Noldor

[Galadriel55]

Originally Posted by Aiwendil

Perhaps the most important event in this chapter is the death of Feanor, quite possibly the most important sub-Angelic character in the Silmarillion. It’s interesting that Tolkien chose to kill off the prime mover of the Flight of the Noldor so quickly. ... It’s very interesting that Feanor’s body is consumed by the fire of his spirit.

It is curious. Feanor starts the great motion, and leaves it to develop and resolve on its own. Maybe Feanor's fea is too bright a flame to last for long in a physical form. That could also be a reason for why his body was destroyed. Feanor is the 'motivator' of history, not it's director, guide, or guardian (that's Gandalf).