Here's why:
* He is initially drawn to the raven's beauty and strangeness. The speaker describes it as "grim, ungainly, ghastly, gaunt, and ominous bird of yore" and "ghastly grim and ancient raven wandering from the Nightly shore." This suggests an initial fascination with the bird's unusual appearance.
* He is somewhat amused by the raven's arrival. He says, "Weakly flapping his wings as I entered, his shadow fell, what seemed to me then, a demon that sits on a chair by the door." This shows that he is still in a state of mourning and perhaps finding a bit of dark humor in the raven's presence.
It's important to note that the speaker's initial reaction is not one of fear or dread. It's more of a morbid curiosity and a slight amusement. It is only as the raven speaks and the interaction continues that the speaker's emotions shift to despair, anguish, and finally, madness.