Why not? It is not an unusual mutation set. Granted that many FReepers are incorrect in believing viruses in general mutate in this direction. Viruses that kill off their carriers at a high rate B4 their carriers can infect many others tend in this direction, but, otherwise it is rather random. Original COVID's low CFR and method of spread make it just about as likely that CFR would go up, be unchanged, or go down. OTOH, greater infectiousness is almost always a "positive" for the virus.
IMO, "Omicron" was just random. While it is true most mutations are insignificant or harmful to the organism reproduced, even with older COVID variants we had many billions of mutations per hour of a not very stable virus.
the issue is twofold - 1) lack of any sequencing history of a direct ancestor of it after 18 or so months ago and 2) the ratio of synonymous to asynonymous mutations is so skewed as to defy odds.