I think it's more about the fact that today for writing we mostly use pencils and ballpoint pens, and not fountain pens (or feathers) anymore. With fountain pen

I think it's more about the fact that today for writing we mostly use pencils and ballpoint pens, and not fountain pens (or feathers) anymore. With fountain pen italic connected cursive is the most natural way to write quickly and cleanly. Writing in block letters with fountain pen is hard, as the tip of the pen goes up or hits the paper on the way down it will leave drops of ink that are very easy to turn into a huge mess. That's why with it you need to be careful and try to write in a continuous movement. With ballpoint pen or ordinary pencil you don't care about the flow of the ink, you can raise and lower the tip anyway you like, hit the paper under any angle, so we all turned into writing the lazy, easier-to-read-afterwords way: using block letters.