A number of American federal holidays fall on a Monday regardless of the date they commemorate. The pattern was created deliberately, and the reasoning was practical rather than historical.
Midweek holidays disrupted the working week
A holiday falling on a Tuesday or Thursday leaves an isolated working day beside it, and many employees took that day off as leave.
Employers therefore lost more production than the holiday itself accounted for, and scheduling around the interruption was difficult across shifts and supply chains.
Moving observances to Mondays removed that stranded day and made the disruption predictable, which is the core of the case that was made for the change.
Three-day weekends had economic backers
A consistent long weekend supports travel, tourism and retail in ways a midweek day off does not, because it allows trips rather than a day at home.
Industries dependent on leisure spending supported the change, and the pattern of holiday travel that followed confirmed the expectation.
Retail promotion has since attached itself firmly to these weekends, to the point where several are known as much for sales as for what they commemorate.
Not every holiday was moved
Observances tied to a specific date, most obviously Independence Day, New Year's Day and Christmas, retain their dates whatever day of the week they fall on.
Where such a holiday lands on a weekend, federal employees typically observe it on the adjacent Friday or Monday instead.
The result is a calendar mixing fixed dates with floating Mondays, which is why the pattern looks inconsistent from year to year.
Federal holidays do not close the country
A federal holiday formally applies to federal employees and to the operations of the federal government rather than to private employers.
States set their own holidays, and private employers decide independently whether to close, which is why observance varies widely between industries and regions.
Banking and financial market closures follow their own schedules, which broadly track the federal list without matching it exactly.
The change had critics from the start
Moving a commemoration away from its historical date was argued to weaken the connection between the holiday and the event it marks.
That objection was strong enough that one observance was returned to its original date after the change, unlike the others.
The debate recurs whenever a new holiday is established, since the choice between a fixed date and a floating Monday determines how it will be observed in practice.