There's also the idea NOT that it was bad when it was written 30 years ago, but that 30 years of patches by people who didn't write the original code mean it's no longer clean code.
Now I work on newer software and I frequently see people making changes without spelling out the rationale, dates, author etc. And it makes it harder to track what has happened and what does the code do exactly. When I tell people to comment it correctly they often reply about - how much time saving can be had by writing a clean code.
Ever moved from Github Issues to Jira/Trello or vice-versa? How about Bitbucket to Github (as I did for my current company)? That's a whole lot of context potentially being lost, either in tickets or PR discussions.
How much of that lost context would have ever been used anyway is up for debate, of course. In my experience the answer tends to be "rarely, but sometimes".
Entropy. It's not our friend. It's why we can't have nice things. Code bases suffer from bit-rot over time.
Minimalistic UIs are great if you're trying to make it simpler for outsiders.
If you have people who understand how to use the software, you can actually cram the UI full of everything you need in a single place.
It's not like I don't get it. I do. Just not 100% of the time.
What I can not dig is how old software prints things to screen. Touch a new dimension, let's recompile the data and re-load the list/entire screen right now! We've never done analytics our study our user base, so the most popular functions are buried 10 levels deep in a menu that re-loads every time you lose your scroll spot! ETC.
If you have spent time in corporate software developed in the WIN 95 days (cough oracle CRM cough) you won't see intentionally brutalist design. You will often see Magyver level hacks stacked through the roof, and software that loads so slowly you can re-load Gmail 3 times before it finishes.
After the latest changea to Gmail I have high hopes that it soon will catch up in terms of slowness :)
Older UIs written in Visual Basic, Delphi, Powerbuilder, or even for text-mode interfaces did not do this, because the frameworks supported refreshing only the changed data.
Look at how emacs or vi works over a 1200 baud dial-up connection. Surprise, it does, because it only redraws the parts of the screen that are changed. These problems were solved in the 1970s and 1980s.
The web broswer has been for most of its existence a really bad way to deliver user interfaces. The zero-deploy nature of it was very powerful though, so people suffered through it. Only in the last few years have browser-based interfaces approached the abilities of native clients.