It had a deadline by which 38 states needed to ratify it. It was ratified in only 35 states by the deadline. And, thus, designated equality for women failed to become a Constitutional protection.
"Many people who followed the struggle over the ERA believed — rightly in my view — that the Amendment would have been ratified by 1975 or 1976 had it not been for Phyllis Schlafly's early and effective effort to organize potential opponents," political scientist, Jane J. Mansbridge wrote in her book Why We Lost the ERA.
In 1980, support for the ERA was removed from the republican party platform. Flash forward to 2018, and we still don't have equal rights for women spelled out in the Constitution.
Enter: The Human Campaign, "an effort to get the ERA passed and ratified by 2020 — the 100th anniversary of the 19th amendment, which gave women the right to vote." The campaign believes that, 100 years after women got the right to vote, it's about time that every protection that men enjoy in the Constitution be applied to women, as well.