Whats so magical about 1y for babys??

Not trying to sounds skeptical, Im just curious why some things are suddently safe after a year of age. Example, certain medicines... baby sleeping with a blankie, honey (i know botulism),etc

But what about a month before 1y? Unsafe.

Suddenly its safe at 1y.

Is there a major leap in development at that age or what?

Thanks in advance! Im super curious