I see you deleted the other post where you asked that question. What about the thoughtful answers you got was unsatisfactory?

Why is right-to-left for WHOLE PARAGRAPHS possible for Arabic languages, but not for CJK nor the Latin alphabet?

It is possible for languages written in the Latin alphabet as well. It's just a pain in the ass to read. You can write cursive Chinese characters top to bottom; there is no vertical cursive script for the Latin ABC. All the connecting nodes are on the horizontal axis. The majority of people are right-handed. So tradition and convention has us reading left to right, top to bottom.

Chinese characters are all square. You know that lined paper for helping kids learn to write? For Chinese it's a series of square cells with star shaped internal markings for aligning the characters. Having them be square means whether you write them vertically or horizontally it takes up the same amount of space overall.

Latin characters are mostly tall and narrow. You can write them vertically but then they will take up way more space than if you wrote them horizontally, so it's annoying and difficult to read. The few times I've seen it in the wild I always have to pause and properly look at it instead of being able to read it as a glance, but that might also be due to me being used to reading English horizontally.

Also, some Latin characters like g or h are taller than the rest, but they extend in opposite directions, which makes it even more difficult to align the characters vertically. Capital and lowercase make this worse. In Chinese, there's no character cases, and characters like 一 are defined as being centred in the square, so having that empty space when written vertically helps with alignment when reading.

Don't know enough about Japanese or Korean to say but I'd assume they're similar.

Also I'd imagine precedence has a lot to do with it too. If it's been written both vertically and horizontally for thousands of years, people grow up used to reading it both ways. Latin languages expect horizontal only so we just don't have experience at parsing it vertically so it takes longer.

It's down to your expectations and practice. We learn to read most Latin based languages left to right. Japanese et al. are learned in a top to bottom order; so, that's what you've gotten used to. Were you to get enough practice, you could learn to read Latin based languages the same way. It would just take time and effort.

It's... just an order. Letters could go diagonally or back and forth, as long as everyone knows how to follow through them. It doesn't matter where they are on the page, and yeah, you can do that with Latin text as well.

Logographs do carry information more densely, since they're not constrained by actual speech sounds, but I don't think that's what you're talking about. (They're a lot harder to learn than a sane alphabetical system, as a tradeoff)

Don't Dead

Open Inside

Possible, but not popular, and therefore strange. Because strange, rare. Because rare, strange. Repeat.

Cursive handwriting/fonts, and ligatures certainly encourage left to right text. Otherwise its just convention?

I suspect it's because the characters in Japanese at least, all take up exactly the same sized box. We find English easier to read when it uses a proportional font, so different letters take up different widths.

Also, Japanese is commonly written top to bottom, left to right, in printed materials but left to right, top to bottom, when handwriting or for casual text. Once in a while, though, they do top to bottom, right to left. I've seen this in temples, so I think it's a traditional format.

In my mind, left to right, top to bottom make sense when writing with ink, because then your hand doesn't smudge the already-written characters. Unless you are a lefty, of course.