If you asked me objectively "do you think it's pretty?" I'd probably say no, but never once has this even occurred me when using it since I'm usually just trying to get work done, which I find it very useful for. It's a productivity tool, not an art piece I'm hanging on my wall.
Nonstandard UIs aren't end of the world, but if possible I don't want the extra cognitive load of interacting with 5, 6, 7, whatever slightly different GUI paradigms.
Like most developers I'm using multiple applications at once. Typically I'm using a terminal, text editor, browser, Slack, email, and maybe a database GUI.
A developer's cognition and cognitive load are limiting factors. Increase my cognitive load by X% and there is going to be a Y% increase in how long it takes me to do something and/or a Z% decrease in the quality of the work. Even if X% is small, it adds up pretty quickly. After all if we are employed full time that is 2,000+ hours per year of work.
Again, not just aesthetics. It's little things like, "does this software support the standard keyboard shortcuts for my system?" If CMD+W closes a window in every app except one that's kind of a pain. Etc.
However, I'd also agree with the GP comment. Its use of SWT ui results in some rather weird oddities. The biggest one is that if we configure gnome to use dark mode in linux, we get this absolutely unusable UI with barely visible text in many places. It becomes very obvious in that case which of the widgets are coming from gtk and which are custom rendered - and the distinction between them is stark.
And there doesn't appear to be a clear way to fix it without actually disabling the dark mode at OS level. I'd be perfectly fine if it used some framework that rendered its own widgets that looked a bit different or even if it ignored the dark mode completely and stayed usable.
People sometimes forget the importance of user experience and it's why some amazing software barely gets used.
Personally I care about aesthetic and consistency but willing to sacrifice depending on what I'm doing.
UI and UX does matter, even when talking about productivity software.
There can also be an element of inspiration and influence. If all my tools are well designed, I’m more likely to set a high bar for whatever I’m building. If I’m using ugly and poorly designed tool. The bar for whatever I’m making will likely drop to the environment I’m around.
A fun representation of the need for such beauty is in the game of Rimworld. In this world, the characters you manage react to the beauty of their surroundings, they need it to be beautiful to a degree, similar to how they need comfort, and recreation. Mood is central to the game, and an easy way to improve it generally is to create a beautiful environment, even if the characters are going to do mundane work like butchering.
Another example is Total Commander. I would buy it if it worked they way I think and had proper whitespace instead of being infinitely configurable and using non-conventional UX defaults (hit R I should jump to the first file staring with R, FFS).
If I have to suffer through this shit then so be it. If I don't have to suffer through it...delete.