That's because it *has* a negative connotation.
doom - definition of doom by the Free Online Dictionary, Thesaurus and Encyclopedia.
"doom
n doom [duːm]
fate, especially something terrible and final which is about to happen (to one)
v
to condemn; to make certain to come to harm, fail etc"
"doom (dm)
n.
1. Inevitable destruction or ruin.
2. Fate, especially a tragic or ruinous one.
3. A decision or judgment, especially an official condemnation to a severe penalty.
4. Judgment Day.
5. A statute or ordinance, especially one in force in Anglo-Saxon England.
tr.v. doomed, doom·ing, dooms
1. To condemn to ruination or death. See Synonyms at condemn.
2. To destine to an unhappy end."
"doom [duːm]
n
1. death or a terrible fate
2. a judgment or decision
3. (Christian Religious Writings / Theology) (sometimes capital) another term for the Last Judgment
vb
(tr) to destine or condemn to death or a terrible fate"
"Noun 1. doom - an unpleasant or disastrous destiny; "everyone was aware of the approaching doom but was helpless to avoid it"; "that's unfortunate but it isn't the end of the world"
day of reckoning, doomsday, end of the world
destiny, fate - an event (or a course of events) that will inevitably happen in the future"
The connotation is there