By definition.
As written above, the present
is burdened by the past. There is an important distinction between disinflation and deflation.
One of the negative effects of inflationary spirals is an inability for firms to enter comfortably into long term supply contracts. Suppliers must predict with greater uncertainty future costs. Their price offerings to buyers intend to protect their investors' interests in maintaining historical profit margins as a percent of sales. In doing so, suppliers offer prices that incorporate their recent history of cost increases.
I note the source of your information is a labor-oriented think tank:
The Economic Policy Institute’s vision is an economy that is just and strong, sustainable, and equitable — where every job is good, every worker can join a union, and every family and community can thrive.
I'd suggest the Kansas City Fed's study on the relationship between margins and inflation as less biased:
How Much Have Record Corporate Profits Contributed to Recent Inflation?
However, the markup itself is determined by a host of unobservable factors, including changes in demand but also changes in firms’ expectations of future marginal costs.