Suddenly getting pentakills?

Okay, so I started the game in September, and for the longest time I have never been able to get a pentakill. In fact, my first pentakill was just two weeks ago, and now I already have 3 (one with Yasuo, one with ADC Ezreal, and another with blue Ezreal).

I don't get it. First I am never seeing them, now suddenly I am getting them fairly consistently (or so it seems). How does that happen?