In fact, why is he not doing that? Since he has unlimited chakra he can make as many bunshins as he wants. Can you imagine 1 million Edo Madara's all with Perfect Susano'o?
It seems that higher intelligence, less they use Kagebushin.
Even that Kagebushing could be used to become more smarter (reading a book in 3 min with 2000 clones at once) and stronger.
I think its because...although he has unlimited chakra..he stays true to what he knew he could do in his prime...he is a dignified warrior...and has honor as a ninja...although the uchihas are emo and want to mind fu** the shinobi world...lol