The terminology difference just depends on who introduced the drink to the region and when. The east coast uses "bubble". West coast uses "boba". If your Chinese community was more Cantonese/HK than Mandarin/Taiwanese, you got "pearl" or "tapioca" instead (because HK also has a sago pearl drink and other tapioca based deserts).

Bubble is technically supposed to refer to the smaller tapioca balls (about the size of a normal straw), boba refers to the jumbo sized balls.

I think boba then became the dominant name because its the shortest and most distinctive.