Board Thread:Theories and Speculation/@comment-26537507-20150930205403

So the way I currently understand the different genjutsu that can be performed with the Sharingan is - Genjutsu: Sharingan, which can be performed by anyone possessing the Sharingan, Tsukuyomi, which can only be performed by Itachi and Kotoamatsukami, which can only be performed by Shisui.

Tsukuyomi's defining feature is that it can alter the victim's perception of time.

Kotoamatsukami's defining feature is that it gives the victim false experiences or overrides their mind with a command.

My question is this: what makes those defining features specific to their respective techniques? What's stopping a Sharingan user with high genjutsu prowess from having a genjutsu that alter's the victim's perception of time? Is there any reason other than Kishimoto being his usual self? 