In fact, the answer is very simple, mainly because most of the history in ancient Greece was recorded by Athenians or authors who used the Attic dialect of Athens.
Why Athenians and not people from other regions? First of all, we need to clarify the geo-linguistic differences. The Greek world is a very general concept. There are also different dialects in Greek, and each city-state has different sayings in a dialect. To put it simply, the Greek people in the Peloponnese region, the western Balkans, southern Italy, and Sicily mainly speak the Doric dialect (Doric) (including Sparta, Corinth, Syracuse, etc.). The Doric dialect has simple and simple grammar, but rough pronunciation and low appreciation. It is mainly used for communication in the above-mentioned areas. Sparta, the most outstanding "military city-state" in history among the Doric-speaking people, had no writing tradition at all. All laws were required to be recited and memorized by the people, so there was no birthplace for historians.
The people of the Attic Peninsula in Greece (mainly Athenians) speak the Attic dialect. The Attic dialect has complex grammar, gorgeous vocabulary and literary appreciation. Higher and therefore ideal for writing in various genres (drama, poetry, history, etc.). Most of the works of famous writers in classical Greece were written in this style. One of the major traditional festivals of the Athenians - Dionysia - one of its important events is the drama competition. Playwrights had to compete with their peers with their carefully prepared works, and the level of literary competition was unmatched in other parts of the classical Greek world. Therefore, it is evident that the literary style of the Athenians was at its peak. Even in the Hellenistic era, after Alexander promoted the "Greek common language" - Koine Greek, many cultural elites were still accustomed to writing their literary works in Attic Greek, and the influence of the city-state of Athens was long-lasting. Decay, timeless and always new.
Further east, there are the Greek residents of the Asia Minor Peninsula, who mainly speak the Ionic dialect. This dialect is slightly softer than Doric, but less grammatically complex than Attic. It has its own characteristics, is simple but not obtrusive, and is an early model for the Attic dialect used by the Athenians. The famous historian Herodotus used this form of Greek to complete his "History". But Halicarnassus, the city-state where Herodotus was born, did not have a profound literary tradition compared to Athens. Therefore, Herodotus lived in Athens for a long time. His lifelong wish was to become an Athenian citizen and promote his masterpieces in Athens.
So, the question is not why Athens preserved so much information, but that the information itself was either written by Athenians or published in Athens by foreigners who admired Athens. From Herodotus's "History", to Thucydides' "History of the Peloponnesian War", to Xenophon's "Greek Chronicles" and "Expeditions", the same strain and firepower were passed down, making the classical era The history of Greece was completely recorded. Not to mention the tragic literature that began with Aeschylus and was passed down through Sophocles and Euripides, as well as the comedic satirical literature of Aristophanes. There are also the philosophical classics of Socrates and Plato... Therefore, the density and quality of the Athenian literature of this era are very high, and it can be said to be a literary model of the classical period. During the same period, the Athenians also defeated the Persian invasion and became a well-deserved "leader (?γεμ?ν)" in the Greek world. In the history of Athens itself, this period of history is also called the "Golden Age". Internally and externally, he looks like a king.
If modern classicists want to conduct written research on everything that happened in the classical era, they cannot avoid the literary works of the Athenians as the literary materials they start with. This is a city-state whose literature has already formed a systematic system. From the fragments of its written records, modern classical scholars can conduct a large-scale restoration of Greece in the classical period and splice together a complete picture of Greece. From this perspective, Athens represents Greece in this era. It’s your freedom whether you value it or not, but without him, modern people’s impressions of ancient Greece would have a lot of information gaps and ambiguities, and the puzzle would not be complete.
Finally, about medieval scholars’ study of Athenian literature. First, it was difficult for other literary works of the same era to compete with Athenian literature in terms of quality and quantity. Most of the written historical materials of the Middle Ages were stored in monasteries. In terms of scale and quantity, it is naturally more likely that the widely circulated Athenian literature will be collected. In addition, literary appreciation itself is an activity with high personal subjective factors, and appetites vary from person to person, so I personally find it difficult to conceptualize.