Let's start with your 100-year ago assumption:
Early 1960s: Author Carmon Hardy cites a poll taken of mainstream Mormons: 40% say they would engage in polygamy if told to by their "prophet."
Then, LDS apostle Bruce McConkie’s book, Mormon Doctrine (pp. 577-579 of 1966 edition, republished 1979 which was approved by the LDS First Presidency…unlike the initial late 1950s version which was not) says that polygamy will return to the Saints before Jesus returns.
"...the holy practice" [of plural marriage]
"will commence again after the Second Coming of the"
[Mormon] "Son of Man and the ushering in of the millennium."
Source: Mormon Doctrine, Lds "apostle" Bruce R. McConkie, Bookcraft, republished, 1979, p. 578 Now we're down to the last 30-50 years...
1998 LDS “Church Handbook of Instructions” for LDS: “A deceased woman may be sealed to ALL men to whom she was legally married during her life.” (“Sealed” in this case = sealed for all eternity to her multiple husbands, making her a polyandrous woman) [This sounds contemporary doesn’t it? If the LDS Church did not want this proxy sealing practice being done in its temples, it has total authoritative ‘say-so’—as it does in shutting the door on proxy baptisms in the cases of Jewish Holocaust victims]
Also current practice:: The LDS Church, as mentioned above, still allows a husband to be sealed in its temple to multiple wives (but only one "on this earth" wife at a time).
Hence, each time we see the bumper sticker, "Families are forever" -- that includes the Mormon belief that if you take wives in serial fashion -- you get them ALL as your eternal wives...provided you're a Mormon in good standing with a temple recommend, that is.
If the Mormon church was serious about "eradicating" future polygamy, it would ban the temple ritual for eternal sealings for a second wife. It doesn't. It views itself as the polygamous “feeder system” for eternal life family life.
Mormonism has simply temporarily "colonized" polygamy.
It seems people don’t want to hear the truth about Mormonism even when they are presented with the truth, kind of like the students at Penn State who didn’t want to hear about their beloved football coach.