First, airliners have complex systems that need to be understood in detail since you can't just pull over at the side of the road like in a car.

Second, newer families of airliners by Airbus and Boeing do have similar systems and often a type rating covers 2 or 3 models now.

Third, each operator has their own standards and practices. In fact, airline operator standards are considered to be more pertinent than general FAA or mfg. requirements.