Memorial Day and Labor day are major shopping days though - a triple overtime requirement would pretty much kill that. The retail employees working that day are often students who want the extra pay, and those shopping are people who appreciate the extra day off to go shopping. Neither of those are particularly "family days".
And for those who are unable (or unwilling) to spend time with family, it's nice that some places are open on Thanksgiving and Christmas.
At *most*, require holiday work give a 25% bonus or an equivalent amount of time off to be used on any arbitrary day in the future. It's enough that there is incentive to let people have the day off, but not so much that entire towns become ghost towns, with only a handful of places being open but so swamped that shopping is a miserable experience.
Walmart would *love* a 3x overtime rule, they'd have no problem staffing stores to the bare minimum knowing full well that they would have to beat customers away with a stick vying for the "privilege" of waiting 3 hours in line to check out... since they'd be the only ones open.