So, let's talk a bit about Marshall Was A Weird Kid.
(I know, you're probably shocked.)
Now, despite the fact that I spent a good chunk of time watching and rewatching a bunch of bad movies, I did, in fact, have other activities, including going to summer camps. One of the day camps I went to regularly was structured thusly: it had two-week sessions, in which you would register for a single course, be it theatre or computers or filmmaking or auto mechanics or what have you. Whatever you signed up for? That was your morning for the two weeks. The afternoon, though, was a little more loosely structured, in that there were a handful of varied activities, and you chose, daily, which ones you were signing up for. One of the most popular afternoon ones was the limited-capacity trip to the local state park for swimming, which my sister made a point of signing up for Every. Single. Day.
That? Was not me.
In fact, my first year there, I was seven, which was itself a bit odd because the camp was for 8-14 year-olds, and I think my mother got an exception made for me because my sister was there as well. So there I was, the only seven-year-old among older kids, looking at choices for afternoon activities, most of which were outdoorsy and/or athletic, to which I was nope. But then one caught my eye.
Seven-year-old me signed up for a goddamn typing class that was mostly populated by teenagers who were there for summer school (the camp was held on the campus of a private school), and I'm pretty sure I was the only one from the camp who signed up for it. But I signed up for it EVERY SINGLE DAY of my first session there.
Every day. Typing. At the age of seven. And this was 1980, so it was on a typewriter. That's how and when I learned, and obviously it was a valuable skill that stuck with me.
BUT, since that's how and when I learned, you're just going to have to accept that a double-space after a period is simply embedded in my muscle memory. It's there, and there's no dislodging it. So there we are.