There just used to be more doubleheaders, but not much evidence that they were tied to holidays. In fact, the Brewers have never played a July 4 doubleheader. They have played a D-header three times on the weekend before, and one of those was in 1992 when the game on 7/4 was rained out and made up as part of a doubleheader on 7/5. They have been off on Memorial Day five times in their history, and three times have not had a game on Labor Day. They have played 10 DHs on Labor Day, but seven of those happened in the 1970s. They had a DH on Memorial Day in 2022 at Wrigley, but even that was a Day/Night schedule where they probably charged separate admissions.
Not sure why some think baseball has more of a responsibility to observe Memorial Day than other businesses. And I'm sure Toronto has no reason to celebrate an American holiday.