Why can't I buy 2 boots

When i get shit on in ranked, I got to a blind pick game and play a stupid build like on-hit or ap . I was always angry that ap didn't make your cleavers OP. Until I discovered the magic of Magic Pen. It was the greatest thing in the world making the enemy go AFK after 3 shotting him with 2 .

But then preseason came, and I was exited to use Comet to make this troll build even more annoying. But for some reason... I couldn't get my boots... Why Rito? Who abused this? WHO STOLE MY FUN?! I didn't hear about any champion using a double boots strat. Inters built most of the time. So why?