Sorry, but there have been just as many, if not more, death metal bands who have released 3 or more good albums as there are black metal bands. Some examples:
Immolation
The Chasm
Morbid Angel
Deicide
Asphyx
Bolt Thrower
Suffocation
Incantation, if "Forsaken Mourning..." is considered as a full-length (which it practically is)
arguably Therion
arguably Pestilence
Deeds of Flesh
Master
Sinister
Vader
arguably Sepultura (three good albums, but two are more speed metal than death metal)
Mortem
Monstrosity
Celtic Frost (again, Monotheist admittedly isn't a death metal album, but then, if you include the Hellhammer stuff, they easily hit 3)
...
and I'm sure there are more.
What black metal bands have done this? Averse Sefira, Sacramentum, Burzum, Immortal, Darkthrone, Graveland, Ildjarn, Beherit, Bathory, Krieg, and Katharsis are the only ones that spring to mind.