Why do many Williams have the middle name Henry?

I’ve noticed that many Williams have, or have had, the middle name Henry. Examples:

-William Henry Harrison, President of the United States (1773-1841)

-William Henry Smith, British bookseller (1792–1865)

-William Henry Vanderbilt, American businessman (1821-1885)

-William Henry Gates III, American software developer and magnate (1955-)

I could give a lot more examples. Is there any known reason why people would combine these two names, or is it perhaps just a coincidence or confirmation bias that I have noted this pattern?

Complete WAG: King William IV was known as William Henry: William IV - Wikipedia. HIs uncle was also William Henry.

Maybe it started by a bunch of people naming their sons after the prince/king, (one of whom became President of the United States and a famous war hero, increasing its popularity) then it continued by people naming their kids after their uncle/grandpa.

Notice the first three examples are from when William IV or his uncle would have been well known and in the case of Gates, he was a III, so who knows when his grandfather was born.

There was also Fort William Henry in New York, which may have given some currency to the combination of names. It was featured in the Last of Mohicans, which was a popular book, no? That also may have added to the popularity of the combination of names.

The fort was apparently named after the younger brother of George III.

William has been one of the most popular boy’s names in England since the days of William the Conqueror. Henry is the name of eight kings. It would be unlikely if you couldn’t find not merely a few but dozens and dozens of people named William Henry over the past 250 years.

News from the Weird has for decades listed murderers with the middle name of Wayne. The list now stretches to 223! I find that many times odder than a few William Henry names.

Why, then, have we not also noticed a bunch of people named Henry William?

ISTM that Robert Bruce is also a common combination. Is there some history behind that?

Not sure if this is a rhetorical question for effect, but for those not aware; yes:

It is merely that for long periods William and Henry were both very popular boys’ names, but that even when this was true, William was significantly more popular than Henry.

For much of the nineteenth century William was the most common boys’ name in the UK. Similarly, in the USA there were times when it was the second most common one (after John). Henry was never quite as popular.

Given this, it isn’t really surprising that lots of boys were given one of the most popular names as their first name and then a slightly less popular name as their second one. (Or that not quite so many were given the slightly less popular name as their first name and the more popular one as their second name.)

We didn’t really come up with a satisfactory theory for James Earl either:

Bottom line, though: Not all parents are as creative as General Sherman’s.

Baader–Meinhof phenomenon plus confirmation bias. William and Henry are both common names. Any given combination of two common names will match a lot of people. Inevitably a few will be famous or successful in their field.

We have. Here’s a few:

Henry William “Harry” Short, pioneer of moving pictures.

"I’m Enery the 8th I am, Enery the 8th I am I am,
I got married to the widow next door,
she’s been married seven times before.
And every one was an Enery, (Enery!)
ain’t no Willy or a Sam (No Sam!).
I’m her 8th old man, I’m Enery.
Enery the 8th I am.

The fastest selling song in history when released in 1965!

Boris Karloff’s real name was William Henry Pratt.

One of my great-grandfathers was named William Henry Blanchard, and shared that name with his father, a son, and a grandson. William Henry Blanchard IV is still alive and must be in his late seventies or early eighties. Next time I talk to my mother, I’ll ask her if she knows why the William Henry combination took root among her ancestors.