Type safety during assignment vs initialization

One of the stated advantages of initializer list syntax is that it improves type safety by prohibiting narrowing conversions:

int x {7.9};   // error: narrowing
int y = 7.9;   // OK: y becomes 7. Hope for a compiler warning

However, AFAIK there is no way to enforce the same check in a subsequent assignment:

int z {7};
z = 7.9;  // allows narrowing, and no other syntax available

Why is type safety during initialization given greater attention by the language design than type safety during assignment? Is narrowing in assignments less likely to cause bugs and/or harder to detect?