Well, good question. Even the Mormon Book of Mormon teaches that...(And Mormons claim they also pay attention to the Bible...where the writer of Hebrews draws the line: "And as it is appointed unto men once to die, but after this the judgment" (Heb. 9:27) [Judgment follows death]
Book of Mormon: Alma 42:16 says that eternal punishment is as eternal as the life of the soul. [It's not temporary]
Alma 34:32-35 says there's no second chance: For behold THIS LIFE is the time for men to prepare to meet God...do not procrastinate the day of your repentance until the end; for after this day of life...then cometh the night of darkness wherein THERE CAN BE NO LABOR PERFORMED. Ye cannot say, when ye are brought to that awful crisis, that I will reprent, that I will return to my God. Nay, ye cannot say this; for that same spirit which doth possess your bodies at the time that ye go out of this life, that same spirit will have power to possess your body in that eternal world. (I cited parts of vv. 32-34)
Both Mosiah 16:11 & 1 Nephi 15:35 says there's only TWO destinations post-death (not a third called "spirit prison"). And the BoM knows only heaven & hell -- no temporary spirit prison (Mormon 9:23; Ether 4:18; Hel. 14:18-19; Alma 3:26; Alma 40:26; 2 Nephi 2:28-29; 2 Nephi 9:16; Alma 41:4; 3 Nephi 27:11,17; 2 Nephi 28:21-22).
If Mormons would only study their own Book of Mormon on post-life...(Smith took much of his early belief system from the Bible before it got twisted)...then they'd see how off-kilter this later-developed baptism of the dead idea was...