Because three speakers mentioned it beforehand.
Because it is essential for the formation of the profession, it gives identity to its practitioners.
Because it relates to work conditions and can exclude people from the profession.
Because we always trust someone with a higher technical knowledge.
The intermediary (translator or interpreter) must be trusted by the other two parties to be doing a good job, because the third parties haven't got control over the interpreter/translator's performance.
It happens with all professions