Board Thread:General Discussion/@comment-26912075-20160401141344/@comment-27241495-20160405055854

Shikai doesn't actually take any effort or power to be active as it is the true form of the wielders Zanpakutou. Shinigami keep them in a sealed/sword form out of tradition or societal demands. The concept of constant release is that the wielder has so much power that it cannot be effectively sealed, or at the very least due to lack of any formal training, they don't know how to.