Because it's funny and works surprisingly well. The idea was to be able to maximize the uptime of Pyke's strong cc. In my experience, Pyke this season doesn't do very much damage even with full lethality because of his gold income nerfs and dies too quickly to be able to make an impact with his crowd control. He becomes an ult bot. I missed broken Pyke mid from season 10-11 and wanted an alternative playstyle that felt good. Iceborn Gauntlet is the only mythic that reminded me of how that Pyke used to play: hitting full team stuns with Flash + E, playing frontline and looking for hooks to build an advantage, and chaining more than 2 R's before getting imploded by a stray Lux E.