No one was particularly interested. People in Constantinople didn’t even know what manuscripts they had! (The major extent Plato manuscripts fir instance are from the 9th-11th centuries, the so called Macedonian renaissance). Westerners became really interested in classical literature after about 1200. Works were preserved, but they often didn’t circulate, to the extent that in the 14th century, Petrarch was able to discover a lost letter of Cicero. As the Turks completed their conquest of the Byzantine empire, Greeks fleeing to west ransacked libraries to find books that would sell in the west, which was mostly Classical Greek, since westerners weren’t interest in Greek tgeologians of the 8th century!

Homer is an exception to this! There are almost a thousand Homeric manuscripts. There are 7 Plato manuscripts. Aristotle was significantly more popular, with almost 300 manuscripts, almost all from the west, and due to Byzantine originals starting in the 11th century

Do these Homeric manuscripts all come the Thrasyllus edition in Alexandria?

It’s crazy that every single one of Plato’s books survived.

I think Plato had a bunch of manuscripts that weren't designed to be public facing that don't exist today. It was like he had stuff for the public, and then he had stuff only for his students. I imagine the tone and narrative voice would have been much different, and that he would have expected much more from his readers in these other works.

I like to joke that the world would be very different if we had Platos lecture notes and Aristotle’s dialogues (which were famous in antiquity)

The manuscripts weren't in Greece. These works were written centuries ago, many of them before the rise of the roman empire. As books were expensive back then, they would often be found in wealthy cities like Rome, Alexandria or Constantinople and often taken as spoils after conquests. The fall of the Western Roman empire additionally meant no one had time or resources to go collecting old dusty manuscripts, but the rising Arabic empires did. Later in the medieval period, notably after the crusades and moor conquest of spain, monks began (re)translating the arabic copies of these works, bringing them back west along with many other novel works, commentaries and inventions.

Wasn't Roman-era writing mostly on papyrus rather than parchment? As papyrus has a much shorter shelf life when stored in more humid climate like Europe (unlike in the desert where it stays intact), if people aren't actively copying them, anything written on papyrus just get lost.