Why was Saudi Arabia only called Arabia before?

As history, it was called Arabian Peninsula, as more of Arab tribe come from here. Yeman, Makkah and Najed "central what is known now as Saudi Arabia"

it's been named Kingdom of Saudi Arabia after King Abdulaziz united all parts, before the name it was named Sultanes of najd,Hejaz and provinces "سلطنة نجد والحجاز وملحقاتها"

Saudi comes from the ruling family name Al Saud