Krayt is one Sith, it is quite different than other orders and he did suffer betrayal. Jacen' reign was too short to let the problem occur. The ancient Sith Empire also involves killing master especially as the Dark Lord of the Sith' apprentice, Sadow killed Simus, Nadd destroyed Sadow's spirit and Kun destroyed Nadd's. In TOR many powerful Sith kill their master because once you do it you can succeed his/her powerhouse, including the Dark Council seat if he/she is a member. Darth Thanaton also said "every sith want to kill their master". Sure it's not all of them but at least the majority in TOR's era wanted to do so.