Steam has had the same UI for the longest time, now. I mean, yes, Valve has added to it, modified it, consolidated things, and so on, but the central UI is still the same now as it has been for years. While this might have worked fine when the selection of games on Steam was more limited and curated, for modern Steam, which allows thousands of games to be sold via it, it’s hard for the UI to keep up.
Which is why it looks like Valve will be reworking the UI of the Steam Store for better discoverability of games, among other things. Speaking at Unite Europe 2017 (via Gamasutra), Valve product designer Alden Kroll showed off how Valve intends to redo the UI, specifically the recommendations system, to improve the discoverability for new games.
Essentially, much like your personal Discovery Lists, it sounds like Valve will give players the tools ti customize the kinds of games the they run into on the store, with tools and filters to enable you to excise software that may be irrelevant to you. Which sounds like a good thing to me- hopefully they don’t go overboard, however, and it is still possible for me to find things outside of my comfort zone!