In French, we say la Bible ; in Italian, they say la Bibbia; in Portuguese, a Bíblia; in Catalan, la Bíblia; la Bíblia in the occitan languages. Whereas as far as I know, the word for book is masculine: le livre (french), il libro (italian), o livro (portuguese), el llibre (catalan), lo/le/eth libre (occitan languages). Maybe somebody could help with Romanian. I ran out of time!
Maybe this Ro. cartea has the same origin as Sp. carta (letter, map, chart) which is from Gr. χάρτης = chart, map from ancient Gr. χάρτις = papyren (roll of) and since the Greeks imported papyren from Βύβλος/ Βyblos, bibel, book, cartea, chart all have this same city as origin