Question: Please see the title.
Assumption: The conductor cannot imitate or rely on previous recordings, especially if a musical work has never been performed or recorded before.
Any musician can master only ≤ 2 instruments virtuosically.
Conductors operate with many more instruments, and so need more musicology and music theory, than soloists.
The complexity of Western orchestral music necessitates research-level music theory and musicology for (improved) analysis and interpretation.
Musicologists dissent about or fail to comprehend objectively some musical works.
4 implies that conductors must understand, at least, academic research-level musicology for constructing an informed opinion of a musical work.
Only a small number of conductors graduated with Doctorate degrees in music, e.g. African-Americans as listed here and such females as JoAnn Falletta, Jane Glover, and Xian Zhang; most famous conductors have not studied beyond an undergraduate degree in music and so would not have studied research-level musicology: e.g. none of the 10 opined by Bachtrack as the world's best in 2015 and per Wikipedia:
A small number of conductors become professionals without formal training in conducting. These individuals often have achieved renown as an instrumental or vocal performer, and they have often undertaken a great deal of training in their area of expertise (instrumental performance or singing). Another way that a small number of conductors become professionals without formal training in conducting is by learning on the job by conducting amateur orchestras, school orchestras, and community orchestras (or the equivalent choral ensembles).