Declining Standards

David J. Garrow's review of Peter Charles Hoffer's Past Imperfect, a book about professional misconduct by historians, plagiarism in particular says Hoffer

...offers an exceptionally astute survey of recent trends in the history profession, and Hoffer’s subtle argument is that the more politically engaged "new history" that has emerged over the past 35 years almost inevitably led to the flock of scandals. It did so in two separate but related ways. First, as the profession became more politicized, and as the major professional organizations took on a more "distinct ideological cast" and moved leftward, a collective desire to make scholarly activity more politically relevant became increasingly pronounced. Hoffer sees the Bellesiles case as one deplorable result; during the Clinton impeachment battle, the embarrassingly partisan behavior of some historians, most of whom had no professional expertise concerning impeachment, was another.

Second, the evolution of the discipline away from the tastes of most nonprofessional readers encouraged the growth of "popular history" as a publishing phenomenon with few ties to the academy. Authors such as Doris Kearns Goodwin and the late Stephen Ambrose may have Ph.D.’s and even university affiliations, but the conception and marketing of their books is a commercial enterprise, not a scholarly one. Their "immunity from close professional scrutiny," Hoffer explains, has further encouraged the absence of originality in most mass-market works.

So on the one hand leftists want to be relevant (not to mention imposing their agenda on the real world) but it's also capitalist desire for profit that makes for declining standards.