Conversation so far:
how did Vaslav Nijinsky's career start?
Nijinsky spent his summer after graduation rehearsing and then performing at Krasnoe Selo in a makeshift theatre with an audience mainly of army officers.
what did he do after that?
These performances frequently included members of the Imperial family and other nobility, whose support and interest were essential to a career.

Question: why were they essential?
Self-contained rewrite: why were the support of the Imperial family and other nobility essential to dancers?