The easiest and most efficient way to force a change in meta is to release heroes that block a certain style of play.
Reinhardt bunkering down with Zarya was pretty hard to punch through, so they released Sombra. They’ve tried to curve dive comp with the addition of Moira and Brigitte, supports that can actively defend themselves if dived by one or two people.
Other heroes were added because of a “gap that needed to be filled” for lack of a better way of phrasing that. Until Ana was released, Mercy was the only primary support. Rein was the only anchor until Orisa was released. There just hasn’t been a need for a new defense because the others can still hold their own.
Let’s not talk about the Doomfist release. He still isn’t even close to being a completed hero.