¡ʍǝuʞ ı ɥsıʍ ı
Word has a function called Title Case that capitalizes every individual word in a sentence. Maybe somebody toggled it on one day and nobody can figure out where to go to change it.
There are times that I wish [Ee]nglish followed the conventions of [Gg]erman, in which all nouns are capitalized. I wouldn’t have to spend time trying to remember whether I was supposed to capitalize “[Pp]resident” or not, and so on. Of course, Mark Twain had the example of having just translated a sentence as “The tiger ate up the unfortunate fir forest”, not realizing that the capitalized “Tannenwald” was a man’s name in this case.
And then, we have CamelCase …
never mind
My son had to learn this in boot camp. It was kind of strange getting his letters - the handwriting was all caps, and very, very neat. I think it’s probably one of the few things he’s written in his life that I could actually READ! 
Am I the only one who remembers the IBM 026 keypunch? If you couldn’t type it in BCD it wasn’t worth typing!
I used to think that was odd as well, until I realised that some message boards automatically ‘correct’ postings made in all caps So That They Look Like This Instead.
I’ve read speculation that some of them do this so that they can easily distinguish the mark’s text from their own.
You would, however, have to spend Time trying to determine which Word in your Sentence was a Noun. Do You really have that Kind of Patience? I notice that You didn’t even try to do that in your own Post.
That hardly makes up for having five ways to say ‘the’ and seven ways to say ‘you’.
It’s been too many years since I’ve studied German, but I can think of at least 6. Poor guys! 
Is it any wonder German is a very angry sounding language?
OK, smartypants. How did you do that?
I’ve done all my handwriting in capitals ever since the day I learned architectural lettering. I wonder if people find my handwriting to be obnoxious.
Could the Commodore 64 have caused some of this? Commodore used it’s own Commodore Ascii, in which the code for upper vs. lower case letters was switched from standard ASCII.
Well, it’s sometimes because they post from secure encrypted government computers, that apparently all have the caps lock on at all times. FORMERAGENT explains in this thread.
(OK, that link is really nothing more than a stroll back into the sordid, bizarre past of the SDMB, way back in '00. While there were the great discussions, sometimes the completely insane ones are the most memorable. Read through it at your own risk.)
But what about people that fabricate words such as ‘allcaps’ and ‘capslock’?
Are they “dumb internet users”?
UUUUU
200903180741Z
TO: BLUFFCITYGUY
FROM: TRIPLER
POST BEGIN
YOUR POST WOULD HAVE LOOKED BETTER LIKE THIS.
END POST
ZZZZZ
Yeah, I get caught up in it too, sometimes. 'Specially when I’m trying to type an “official” email. I think it’s easy to get caught up into. . .
Tripler
ZZZZZ
I write longhand exactly the same way. I find that it has even invaded into my cursive. My 7yo son is learning cursive now and I had to get on the interweb to find out how to correctly form a capital Q, G, T, and S in cursive as I just don’t bother anymore.
I took a class in interior decorating (don’t laugh, I needed to fill out my schedule somehow) and we were also instructed to write this way for our drawings. For a while, I wrote everything this way, but soon went back to my printed capitals and cursive lowercase way of writing.
In regards to the OP, all caps was easier to read on the very first online services I had access to. I was on QuantumLink and then U. S. Videotel, FTR. I used my Commodore monitor on QLink and the USV service had its own monitor. Both monitors were not what you’d call hi res.