Why are loaded liquid tank vehicles especially prone to rolling over compared to many other types of cargo?

AAMVA CDL Manual, Section 8.2.1 (High Center of Gravity), p. 8-8-1, Figure 8.1

Understanding why tankers roll over more easily helps drivers anticipate situations (curves, lane changes, sudden steering) where extra caution is needed. This knowledge underlies nearly all of the tanker-specific driving rules that follow in the CDL manual.