There are a few factors that contributed to the Byzantine Empire becoming more Greek than Roman:
1. Location - The capital of the Byzantine Empire was Constantinople, located in modern-day Turkey. This put the empire physically closer to Greek populations and further away from Rome and Latin-speaking areas.
2. Demographics - The majority of the population within the Byzantine Empire spoke Greek, not Latin. Even before Justinian's time, most citizens were ethnic Greeks who spoke Greek as their primary language.
3. Cultural differences - Over time, the Greeks and Romans developed distinct cultural identities. The Greeks strongly identified with their Greek heritage, language, and traditions. This Greek identity persisted within the Byzantine Empire.
4. Loss of Western territories - As the Byzantine Empire lost control of territories in Western Europe to Germanic tribes and the Muslim conquests, they lost Latin-speaking populations. This further tilted the demographic balance toward Greek speakers.
5. Justinian's reign - Justinian himself was fluent in Latin but had a Greek mother. His efforts to reunite the Eastern and Western Roman Empires brought him into closer contact with Greek political and religious culture. This likely increased Greek influence during his reign.
In summary, a combination of geographic, demographic, cultural, and political factors pushed the Byzantine Empire away from its Roman roots and toward a predominantly Greek identity over time. Justinian's reign marks a turning point when even the emperor no longer spoke Latin as a first language.