"...then it is soooo easy to change to a better block chain."

Not so much. All it takes to destroy a given crypto is targeted censorship - something they demonstrably effect with facility. Absent additional supportive decentralized technologies, such as mesh networks that aren't censorable, any single industrial mechanism is able to be captured easily.

The real power of decentralization is concatenation across fields. Centralized bureaucracies are inherently incapable of focusing their power on amorphous and distributed targets.