Easier and faster for late-antique scribes to write. Later, Charlemagne thought that it was a good idea. The rest is history (oh yeah, Cosimo di Medici and the humanists had a hand in codifing it, too).

Not all writing sytstems have multiple cases, though.

Alessio Leonardi, my absolute favorite graphic designer ever, gives the following description on pages 101 and 102 of his book From the Cow to the Typewriter; the (true) History of Writing. https://www.buymyfonts.com/shop.php

Hah.. Thanks, Dan, for posting these.. Fantastique..

I believe there is some well documented evidence that script-like (miniscule) faces were used in the tier structure of the Phoencians, Egyptians, Greeks, and Romans, etc where they served as sort of the low end status form of written communication

http://www.thebritishmuseum.ac.uk/compass/ixbin/hixclient.exe?_IXDB_=compass&_IXSR_=qo8&_IXSS_=_IXMAXHITS_%3d1%26_IXFIRST_%3d1%26_IXDB_%3dcompass%26%2524%2bwith%2ball_unique_id_index%2bis%2b%2524%3dOBJ1461&_IXFIRST_=1&_IXMAXHITS_=1&_IXSPFX_=graphical/full/lg&_IXimg=ps240191b.jpg&submit-button=summary
These are from your part of the world, it might not be an answer your question directly but I think they are worth looking at. It reinforces the point Dan made. Apparently the Romans, when pulling out of the fort, burnt correspondence and the fire failed to burn everything (the material is wood) and these were found under ashes.
Tim