Can anybody explain why both Trump and Biden blocked this amendment, especially it was part of Biden's election promises?

"After the last state ratified the ERA in 2020, the Trump administration blocked it on a technicality and prevented it from being added to our Constitution as the 28th Amendment. The Trump administration also fought against the ERA in two federal lawsuits (one filed by me). Women were then encouraged to vote for Biden/Harris during the 2020 presidential election because they claimed to support Women’s equality, but when Biden took office in 2021, his administration continued to block the ERA and continued to fight against it in the two federal lawsuits."