How was it a game changer? We had handheld gaming units before steam deck and the rig ally outsells the steam deck.
The handheld was just a market that didn't have much competition at the time. Which likely made it easy to justify it as a business decision for Valve.
Such an incredibly pro-consumer move by a company with such a big market share. Anti-enshitification. Hard to imagine any other big name company doing something so radically positive.