Perhaps Hashirama has experience combating the Sharingan.
I feel like Madara could have just used genjutsu on Hashi during every one of their fights. Why did that never happen?
Harishimha is an experienced Senju whom has battled several Uchiha clan members before so, He'll be capable of avoiding Genjutsu as a whole, plus his chakra level is insane and he also has Wood sage mode
Hashirama's Chakra control was so perfect he became immune to Tsuki.
Come on he summoned 1000 hands around 100 times bigger than P.S
This is just a theory but having very powerful chakra along with incredible chakra control prevents genjutsu usage. Genjutsu disrupts chakra which having powerful chakra and powerful chakra control prevents that. Madara couldn't use genjutsu on Edo Hashi because I don't think genjutsu works on edos
Well, Kotoamatsukami apparently worked on Edo Itachi.