No idea, but it's something I've been thinking about ever since my parents dug out an old school journal from when I was younger and they were laughing about the stuff I wrote in there... The first 50 pages or so were full of laughably simple phrases like, "played with sand" or "i like computers".
Later in the journal my writing "improved". Instead I might write, "Today I played in the sandpit with my friends."
I vaguely remember my teacher telling me I needed to write in full sentences, uses the correct punctuation, etc. That was the point of these journals – to learn how to write.
But looking back on it I started to question if I actually learnt how to write? Or did I just learn how to write how I was expected to?
If I understood what I was saying from the start and I was communicating that message in fewer words and with less complexity, was it wrong? And if so wrong in what sense?
You see this with kids generally when they learn to speak. Kids speak very directly. They first learn how to functionally communicate, then how to communicate in a socially acceptable way, using more more words.
I guess what I'm trying to say is that I think the fact you can drop capitals and communicate just as effectively is kinda interesting. If it wasn't for how we are taught to write, perhaps the better question to ask here is why there are even two types of every letter?