In that sense -as others have mentioned-, it's functionality much closer to a 'Video Patreon' than it is to say, a youtube alternative (AAMOF they've explicitly mentioned that several times)
When seen through that lens, it becomes apparent that "looking good" isn't really all that relevant, I mean, would the way patreon looks prevent you from supporting your favorite creator? probably not.
PS: Of course I get that good UI/UX is a must these days, my point is that they probably have much higher priority (not to mention mission-critical) tasks on their to-do list right now.
Once you view a stream the only things you see are the video player, details about the streamer, and chat.
Not sure what you imagine could be better, but if you want to know what really bad UI looks like, check out Mixer.
Floatplane has made a very conscious decision not to influence the user's decisions on consuming content; there's no algorithm, recommended videos, or trending page. you just have access to the videos of people you want to support.
"Good looking" is far from the most important thing in a web site like this. But it is hard to argue it isn't relevant.