> nobody knows how to write emails anymore
I think the problem is bigger than that, nobody knows how to write anymore. In the past, people wrote in handwriting ('cursive' in America) on plain paper (with no guide lines) and with a fountain pen. We didn't keep what they put in the bin, so there is some survivor bias, however, when I look at letters my ancestors wrote, I am amazed at how few corrections there are.
As I understand it, we have two thinking modes, there is the quick thinking by reaction and then there is the more convoluted 'slow' thinking where we use logic and reason. I am not convinced that too many of us have the skill of putting 'slow thinking' into written words, or the desire to put complicated ideas to paper.
So, what changed?
SMS and Twitter did have a text limit of 140 characters. This was not good if you need 140 characters just to introduce what you have to say, however, it didn't take long for people to adjust. Spelling was no longer important, neither was punctuation or sentence structure.
Soon this 'communication with grunts' replaced eloquence, and we degraded our collective literacy. Nowadays you can't write beautiful emails to people as it is a bit of an imposition, you have spent maybe hours crafting words, they only have seconds to respond due to the all-pervasive 'busy lives' excuse, and they definitely don't have the ten minutes it takes to read your carefully written words. Hence, writing in full just means you get ghosted at best.
Clearly there are more books being written than ever. School assignments also get done, same with work-related documents. However, the craft of writing has become even more professionalised, even though everyone can open some type of word processor, pick up a dictionary and write something awesome without having to get the old fountain pen out.
As for the post, what if I was the son of the author, and I had to tidy up his affairs after some tragic accident? All of those emails would be gone, lost to posterity and only the emails from the bank read (because money). All of that obsession on having every email organised for the last four decades would be for nothing, outside of the mind of the author.
Most people used to be illiterate a few generations ago and then only had a handful of books in the house, like the Bible and some other staples, and their letters were full of spelling mistakes, and clumsy writing and bad letter shapes. This is also seen in reddit translation requests of postcards and letters.
Your impression is based on immense selection bias. Maybe your ancestors were in the top percentiles, nobles, aristocrats, or even just doctors, academics and priests. But up until the early 20th century the vast majority were farmers and then they were factory workers.
Great writing and abundant reading was always very niche.
Selection bias means that we don't have the sheer volume of printed material that there once was, as in pulp fiction novels, not to mention the newspapers and magazines that used to be in such abundance.
Where you lived made a difference. A rural Catholic area was not what you wanted. In the city with protestant ethics, things were a little different, more than one book was permitted.
Fortunately there is a lack of aristocracy in my known ancestry, so factory workers over the last century, and reading was the thing for them, including all of the difficult books, even though none of them had much in the way of education, just basic schooling and working for Ford in ye olde factory.
Agreed that before the 1900s there were literacy issues. However, empire has always needed vast armies of clerks and record keepers, so literacy has always been important, just not for everyone.