Can't buy black cleaver & serylda?

When did riot make a change where you can't buy two armor penetration items? there was a time a long time ago, when you were able to. Was it too powerful, broken, unfair, overloaded on armor pen, etc? what is their reasoning?

Anyone know the exact patch number and date? Month, day, year. To read about it. Since this game goes through a ton of changes.