Mostly because of Olson's role in Bush v Gore in 2000.
Levin never mentions that Olson himself, a thorough-going amoral libertarian who worshiped freedom above all other things, thought his greatest legacy was overturning California's same-sex marriage ban, glowingly covered by WaPo:
Mr. Olson said he considered his greatest legal legacy to be his role in invalidating California’s Proposition 8, a measure banning same-sex marriage that had passed in 2008 with 52 percent of the vote after the state’s Supreme Court legalized same-sex marriage.
He had come to the case in a most unlikely way, through Rob Reiner, the film director and liberal activist who was among those intent on reversing the recently approved proposition.
Reiner had a decidedly low opinion of Mr. Olson, stemming from what he regarded as Bush’s ill-gotten 2000 election win. But Mr. Olson told Reiner that he found Prop 8 “wrong, morally and legally,” and Reiner was convinced that the lawyer could appeal to conservatives.
“It is a conservative value to respect the relationship that people seek to have with one another, a stable, committed relationship that provides a backbone for our community, for our economy,” Mr. Olson later told the Los Angeles Times. “I think conservatives should value that.”
Mr. Olson endured taunts from former supporters on the hard right, some of whom unleashed homophobic vitriol. Conservative talk-show host Rush Limbaugh denounced him on the radio. Others declined invitations to dine at his home near the Potomac River.
Mr. Olson also said he wasn’t trusted by gay rights advocates who feared that Americans were not ready for same-sex marriage and that challenging the ban in court might backfire and set back the cause for years. Some marriage-equality supporters said they feared that Mr. Olson took the case intending to throw it, a notion he dismissed. “I don’t take cases to lose,” he declared.
In part to allay those suspicions, Mr. Olson asked David Boies — an impeccably credentialed trial lawyer and a registered Democrat who had argued Gore’s case in 2000 — to take the marriage case with him. To the Los Angeles Times, Mr. Olson explained that the case was not a partisan matter but rather one about “human rights and human decency and constitutional law.”
Mr. Olson delivered the opening statement on Jan. 11, 2010, in U.S. District Court for the Northern District of California.
“In California,” he said, “convicted murderers and child molesters enjoyed the freedom to marry,” he said. “What Prop 8 does is label gay and lesbian persons as different, inferior, unequal and disfavored. It says to gays and lesbians, ‘Your relationship is not the same.’ … It stigmatizes them. It classifies them as outcasts. It causes needless and unrelenting pain and isolation and humiliation.”
Judge Vaughn R. Walker, who heard the case without a jury, ultimately found Prop 8 violated the guarantee of equal protection under the law. Although the decision had an immediate effect only in California, it was a major rallying point nationally for gay rights proponents.
In 2013, the Supreme Court avoided ruling on the merits of same-sex marriage, although it affirmed Walker’s decision, finding that opponents of same-sex marriage lacked standing to defend Prop 8 in court.
Still, the win was credited with paving the way for the Supreme Court’s 2015 ruling in Obergefell v. Hodges, which extended marriage equality nationally.