Judaism
The main reason is geographical and historical isolation. But “isolated” does not mean they had absolutely no contact with other Jews.
🧠 Imagine the situation
Think of the Beta Israel as a Jewish community living in northern Ethiopia, far from the major Jewish centers of the Middle East.
For many centuries:
Ethiopia 
⬇
Red Sea 🌊
⬇
Arabian Peninsula / Middle East
⬇
Other Jewish communities
Crossing these regions was difficult, especially before modern transportation.
1. 🗺 Geography made contact difficult
Ethiopia is separated from the main Jewish population centers by large distances and difficult terrain. The Red Sea also separated Ethiopia from Arabia.
So regular communication with Jewish communities in places such as Egypt, Yemen, and the Middle East was difficult.
2. ✡ They developed their own religious tradition
Because contact was limited for a long time, the Beta Israel developed and maintained their own tradition, called Haymanot.
For example, their religious system traditionally did not follow the Talmud in the way Rabbinic Judaism did.
Instead, their religious life centered heavily on the Orit and their own oral traditions and religious leaders, the Qessim.
3. ✝ Ethiopia's political and religious history also mattered
After Christianity became dominant in the Aksumite kingdom, Jewish communities existed within a predominantly Christian Ethiopian society.
Over subsequent centuries, there were periods of conflict and persecution involving Christian rulers and Beta Israel communities. This could further limit their interaction with outside Jewish communities.
4. 📖 They didn't simply "forget" Judaism
This is important.
Their isolation did not mean:
"They forgot Judaism."
Rather, they preserved their own form of Jewish religious tradition while developing separately from Rabbinic Judaism.
Think of it like two branches of the same tree:
Ancient Judaism
│
┌────────┴────────┐
│ │
Rabbinic Judaism Beta Israel
│ │
Talmud, etc. Haymanot
Orit
Qessim
So when modern Jewish communities eventually had greater contact with Ethiopian Jews, they noticed that Beta Israel Judaism had developed differently.
🧠 One sentence to remember
Beta Israel became relatively isolated because Ethiopia was geographically distant from other Jewish centers, communication was difficult, and historical circumstances—including living within a predominantly Christian Ethiopian society—limited sustained contact; consequently, they preserved a distinctive Jewish tradition called Haymanot.