Are you right handed? Have you ever tried to paint something horizontally, using a brush .... or wipe the wet window with a towel? How is it more convenient to do? It is convenient to do right to left. But why then do we write from left to right, and the Jews and Arabs, on the contrary. It looks like they use opportunities more intelligently.
I'm sure all the answers lie in a simple Google search but my lazy guess is when using a hammer and chisel it was easier hammering with the dominant right hand making chiseling easier going from right to left. Once wet ink was used I can see where it might make sense to write right to left, or even top to bottom, but for a majority of right-handers it would be left to right. I remember in school learning cursive and being right-handed it was no problem but my best friend being left-handed it didn't work well for him...no easy way to write like right-handers...and of course impossible when using wet inks. But teachers then, and perhaps today, had no solution for left-handers...
I learned the Arabic alphabet pretty well. It's not difficult to write that way once you adjust to it. Feels normal.
Traditional Chinese and Japanese writes vertically down in lines, with the lines following from right to left. Supposedly that facilitated writing with a brush in the right hand while continually unrolling the paper or scroll with the left. Another likely reason was that texts were sometimes written on rolls of bamboo strips tied together. (Obviously then it would make sense to write vertically, assuming the scroll of bamboo strips would be rolled horizontally) Now the modern form writes in horizontal lines, from left to right, like European writing.
The traditional British handwriting "rondo" is also written from left to right, but there is no inclination in this handwriting .. In British schools, in the middle of the 20th century, only such a style was accepted to be correct ... You are talking about the "convenience of writing a letter" But, I believe that it is not the most important thing to write from left to right. Jews and Arabs are not stupid. And they love convenience.
I'm left handed, I had a lot of difficulties to write correctly, and I tend to get my hand tired quickly when I must write a lot.
When learning cursive the letters were not vertical...they had to be slanted about 15 degrees towards right of center. My left-handed mate did well 15 degrees left of center but the teacher failed him. So he would push his elbow out as far as he could, and then bend his wrist back towards him, and then try to make characters that were slanted 15 degrees right of center...he could manage but it was as you say quite uncomfortable...
Yes, some people says I have a pretty writting, but when I had 2 hours long courses, I left the courses with my hand on fire. I didn't had the money to buy one of those small computer many students use now. It's a small disadvantage to be left handed, but nothing unbearable.
It's pretty easy actually to answer that. They had low self-esteem, never did anything useful, never built anything, and went and tried to feel special by adopting an absurd set of laws and principles. The same way the English drive left, and the Americans use the inferior Fahrenheit. Look at them closely. They all try and justify bad decisions using a very shallow explanations that don't hold together. English when asked why they drive left they said that when Knights rode horses during the Medieval times, they pulled their sword with the right hand when kneeling on the left knee, hah. And Americans say they use Fahrenheit because it's better. It's how the body feels the weather, so between 100°F and 200°F is a better measurement. It's important we specify that. With Fahrenheits water boils at 212, and freezes at 32. It's just stupid and hard to remember and measure. With Celsius, at 0°C water freezes, at 100°C it boils. Round numbers are best to remember. Hot summers are 30-35°C, spring and fall are 15-20°C, winters are 0-10°C, and below the zero, the rain becomes a snow. Canada converted to the metric system in the 1970s... England in 1965. And pretty much the rest of the world. I guess it is not so diffucult. The same way Muslims will always justify that Islam is a religion of peace, and Bulgarians will always say that they invented the computer, when John Atanasoff was born in the US and didn't know a word of Bulgarian. Worse than Nina Dobrev. She at least speaks some Bulgarian. They'll write from right to left even if it's harder than carrying a bag of stones from a mountain in Switzerland. It's how some people are. They argue, they twist, and at the end they lose.
Leonardo Da Vinci was left handed and did that. It's hard to do and you can do that only for yourself because you would be the only one to understand yourself. It's already problematic enough to read handwritting when it's in a regular sense.
I'm thinking we should be able to write in whatever way allows us to clearly communicate...left to right, right to left, L-R then next line R-L and so on, or even in circles, as long as it's intuitive to the reader. I can compare this to how we talk in which our teachers don't demand we talk at a certain octave at a certain rate, etc. And it depends on why we are writing or to whom we are writing...if we are writing for our own use then who cares, but if we're trying to communicate with others then they must understand what we write or have easy translation. I think it is the clarity and consistency of the characters more than L-R or R-L that makes a difference...I would have no problem reading Da Vinci's writing...
It would create problems for people with dyslexia. We can't satisfy everybody. I think the best would be from up to down. But I doubt that everybody will change their wrighting system only for a potential benefit for left handed people .
The writing system won't change but it seems there are good reasons to allow some creativity and not have teachers so rigid about the right-handed style...