Steam does a few things at once to make this system work so well. There's just Wine itself and Valve-sponsored work and improvements to it, the automatic usage of DXVK and similar newer translation-to-Vulkan systems for DirectX support vs. Wine's classic alternatives, there's Steam automatically creating wine prefixes per-game, there's a separate but related container system, the "Steam Linux Runtime" that allows both Proton and native Linux games to have a stable, known set of libraries to target and support vs. the dizzying array of distributions and versions that otherwise typifies supporting Linux.
On the other hand, having that corporate support and isolation from the system sometimes cuts both ways: stock Proton often has worse support for audio and video codecs than a classic Wine install with the proper system libraries, because Valve actually has to worry about patents and licensing for them. They've come up with a system where the layer they otherwise use for sharing cached shaders can also share transcoded media files, but it's not always a seamless experience.
On the other hand, having that corporate support and isolation from the system sometimes cuts both ways: stock Proton often has worse support for audio and video codecs than a classic Wine install with the proper system libraries, because Valve actually has to worry about patents and licensing for them. They've come up with a system where the layer they otherwise use for sharing cached shaders can also share transcoded media files, but it's not always a seamless experience.