Some powers within the Bleach series are simply just too dangerous, too powerful or too unpredictable to be used in the presence of others. Sosuke Aizen barred Ulquiorra Cifer from releasing his Resurrección, Murciélago, under the ceiling of Los Noches, while Shunsui Kyoraku is discouraged from using his Bankai, Katen Kyokotsu: Karamatsu Shinju, due to the volatile nature of its power. However, Shinji Hirako's Bankai is banned in the entirety of the Soul Society due to the immense danger it poses to any caught within its indiscriminate sphere.
Source：https://www.cbr.com/bleach-shinji-hirako-bankai-why-banned-in-soul-society/
