Of every single comment in this thread, yours is the one actually addressing the most important factor that influenced this custom. This was imposed by schools who only had typewriters. Newspaper and publishing didn’t even think about this because on printing plates they had kerning to worry about when setting each letter.

Same with the 1 and a half or double space between lines. Most people never consider to think that it was taught that way so teachers had space to write notes on your papers. Books and magazines don’t need that much space and it actually looks ugly and makes reading harder. Outside of schools, typography is wildly more diverse and adaptable than the narrow habits taught to the amateur touchtypist.