This is mostly because of the Hyper Roll strategy, which focuses on utilizing the RNG mechanics to optimize the number of level 1 champions you get.
How the champion pool works is that the higher the level you are, the higher the chance you have of finding a higher level champion and the lower a chance you have of finding a lower level champion. Level 5 tends to be a sweetspot for finding these level 1 champions in terms of both the gold you have and the likelihood that you'll get the level 1 champions, and 3/1 is the last round at which you can be at level 5.
The strategy is that you save up as much gold as possible until 3/1, making sure that you are buying no experience, can minimize the damage you take (if not outright win the early rounds), and can beat Krugs at 2/6. Then, at 3/1, you purchase any level 1 champion you find and focus on getting 3-stars on as many of your champions as possible. You purchase the extra level 1s to dilute the pool of champions you can find, and if you find a level 3 you have a huge power spike that can carry you to the end of the game, in some cases guaranteeing a top 4 finish.
Biggest downside is that if multiple people are taking the same champion then it's really hard to hyper roll for that champion because there's a finite number of each champion, with Predators and Woodland Druids being the hardest to hyper roll for since their strong early game and lack of late-game scaling makes it easy to justify hyper rolling with those comps to get some sort of late-game power out of it.
In my most recent win (and currently only ranked 1st place victory, shoutouts to all my fellow bronze scrubs), I looked to hyper roll a Vayne in a light comp. I ended up finding around 4-5 Vaynes before Krugs, and at 3/1 I started rolling all the way until I found the Vaynes I needed. I stacked a couple items on her (Statik Shiv and Phantom Dancer, I had no NLRs or Negatron Cloaks so I couldn't give her sustain outside of light bonuses), paired her with a few other light champions (including level 3's on both Jax and Soraka, but also a level 2 Aatrox and Yorick), added Kindred for level 2 Ranger, added a Yi with Zeke's Herald and Locket of the Iron Solari (don't judge, it gave mystic for Soraka, shadow for Kindred, and blademaster for Aatrox, and it came with the Herald and the Elder Dragon gave me Locket), and suddenly she was just chunking out damage while being borderline unkillable thanks to the Jax frontline, the light trait bonus, and the Phantom Dancer (which was extremely useful because someone decided to build assassins).
What helped was that I was one of two people going light and the other person didn't have a Vayne, so it became rather easy to justify hyper rolling for Vayne.