> what was the justification for imposing such a restrictive rule?

This is a totally worthless question to ask about a law or rule.

The general form would be "why was the law created?"

And of course, there's never a law with the (disclosed) purpose of killing all kittens, giving money to friends or destroying an enemy. On the contrary, every law is always spun on some kind of "will you think of the children".

The only good question you can ask about a law:

"What are its consequences?"

Interestingly, your first question was more in this sense.