"Jack and Jill went up the hill...."
They experienced accidents. Jack's was reported to have a traumatic encephalopathy; Jill's was unspecified.
This is all part of a consistent pattern; there almost seems to be a conspiracy of neglect behind it.
After all, look at how many senses is the word jack used:
a) As a device for lifting, like for automobiles;
b) As a flag that flies on the bow of a ship;
c) As a plug or connector for electric circuits;
d) As an interlinear translation.
Someone who has multiple skills is "a jack of all trades." Multiskilled Jills are unrecognized.
Jack must be someone that is deemed important to know. After all, there's scorn in the expression, "You don't know Jack!" There's no stigma attached to not knowing Jill.
Hotels and resorts are known to jack up their prices during peak demand times. But no one jills up or jills down their prices!
And when oppressive governmental thugs get outfitted, part of the package is their getting jack boots. Jill boots are never offered as an option, however stylish they might be.
Jackhammers are used to break up concrete. But try to purchase a jillhammer! That would raise eyebrows at Home Depot.
An older generation of kids played at jacks. No one played jills.
Hollowed out pumpkins are jack-o-lanterns; those with obviously female features are not jill-o-lanterns!
Female loggers are not known as lumberjills, even though they're okay, and they may also sleep all night and work all day.
Speaking of playing, there are four jacks in a deck of cards. Sadly, no jills.
And while dateless guys might have their self-gratification option still available, girls are not known to jill off.
On the other hand, there's yellow jack, otherwise known as yellow fever. This disease was formerly a scourge of New Orleans, spread by the Aedes mosquito. At least I can say that none of my ancestors died from yellow jill.
While TSA may have to worry about planes being skyjacked, no one is particularly concerned about them being skyjilled.
And some inexpensive apartments have Jack and Jill bathrooms. Knowing the tragedy of the commons, these are rarely kept clean by either user.
Road Trip, a few of the people I met
12 minutes ago