Por que os companheiros tinham uma posição social tão alta?

Eles são muito mais do que prostitutas.

Da Pirilamia Wikia :

Registered Companions are culturally well-educated with training in a number of areas, including psychology, music, fencing, and languages, as well as unarmed martial arts. On the "core" planets, Companions were typically trained from a very young age.

Isto não é irrealista : compare com o oiran da vida real, algumas cortesãs japonesas dos quais tinha status bastante elevado na sociedade, sem dúvida muito mais do que um bandido, contrabandista e 'ladrãozinho' como Malcolm Reynolds teria:

Compared to yūjo (prostitutes), whose primary attraction was their sexual favors, courtesans were first and foremost entertainers. In order to become an oiran, a woman had to be educated in a range of skills, including the traditional arts of sadō (Japanese tea ceremony), ikebana (flower arranging), and calligraphy. Oiran also learned to play the koto, shakuhachi, tsuzumi (hand drum), and shamisen. Clients also expected them to be well-read and able to converse and write with wit and elegance.

Within the pleasure quarters, courtesans' prestige was based on their beauty, character, education, and artistic ability, rather than their birth.

The highest rank of courtesan was the tayū (太夫?), followed by the kōshi (格子?). Unlike a common prostitute, the tayū had sufficient prestige to refuse clients. Her high status also made a tayū extremely pricey—a tayū's fee for one evening was between one ryo and one ryo three bu, well beyond a laborer's monthly wage and comparable to a shop assistant's annual salary.

Dadas as semelhanças entre a descrição acima do oiran e algumas das informações que Inara nos conta sobre os Companheiros - mesmo em detalhes como a cerimônia do chá - parece provável que Joss Whedon tenha baseado conscientemente o sistema Companion no oiran da vida real. Mas ainda não achei nada canônico para confirmar isso, então eu fiz uma pergunta sobre isso para encontrar fora.

Embora não haja dúvidas de que os companheiros são profissionais do sexo, eles são muito mais do que isso.

De Wikipédia (re Inara)

... Companion, a high-society courtesan licensed by the Union of Allied Planets (the "Alliance").

In Alliance society, Companions are part of the social elite, often accompanying the wealthy and powerful. There is considerable ritual and ceremony surrounding their services, which appear to extend beyond sex to nurturing psychological, spiritual, physical, and emotional well being.

Companions do not view themselves as prostitutes and are insulted by the suggestion.

Companions choose their own customers, and to be chosen by one is considered a great honor and status symbol, as those chosen must be both wealthy enough to afford a Companion's often steep price and desirable enough to attract one

Assim, um acompanhante é um profissional legal altamente qualificado que passou por treinamento extensivo nos serviços que prestam e, assim como qualquer outro profissional muito procurado, são bem-vindos de acordo.

Observação também que eles escolhem quem eles terão como clientes, e não o contrário. Eles imbuem status de seus clientes , tornando-os altamente valorizados.