Even though I'm credited as being a Content Developer on the CubeCraft team, I'm actually a game design graduate from Breda University where I specialized in technical design. I agree with you though, in a larger company you'd have a dedicated UI/UX designer working on this sort of thing. Either way to give you some history;
The big UI update we did in 2021 was very focussed on mobile users, but one gripe I had was with the bulky category buttons, they never sat quite right with me. (and I made them) Besides that, community often complained about their performance, which is why I was motivated to improve both it's UX and performance. To quote Shigeru Miyamoto
'A good idea is something that does not solve just one single problem, but rather can solve multiple problems at once.'
So for the past 4 months I've been toying with different ideas and we eventually landed on this implementation. Because most players don't own that much loot, and might not know which loot types are used in what games, we decided to bundle loot together by game. With the old menus that wasn't really possible, because you'd be scrolling for an hour before finding the category you're looking for. Another advantage of the text-based dropdown layout is it's flexibility. We can use our custom glyphs in the category titles and each category can have sub-categories as well, like you see in the main loot menu.
As expected, there's a lot of criticism regarding these changes and I'm reading a lot, if not all of it. What's important to me here is figuring out what's frustrating players and finding ways to move forward while alleviating that frustration. Don't worry, I'm not taking any comment personally, haha. Honestly I'm just glad to see people are so passionate about the CubeCraft. Generally I'm not very active on the forums or Discord, but trust me, I'm always reading messages and listening to player feedback. Of course it's impossible for me to make something everybody loves, but I'll try my darndest to make the server better one small step at a time