Being the most favorable game market does not mean "there is no competition". It's just the competition is doing it wrong so everyone flocks to what they like or have stuck with.
I'd argue Steam is probably the among the most competitive digital marketplaces. No games are sold above their MSRP, there are frequent deals that drastically cut the prices, and the UI is clear & comprehensive.
Yeah it’s a bit convoluted and there are lots of things hidden in strange places imo. Steam deck is great tho, and the ui works well for a handheld in that context. On the other hand when I try to use big picture mode on my windows handheld, steam refuses to connect to wifi so there’s that 🤷