What is the Ultraviolet Catastrophe?

Science Asylum is great, but I dislike the 90s educational show presentation format. An absolute gem I've stumbled across is ScienceClic: link They have amazing presentations on Relativity, my favorite being: "A new way to visualize General Relativity" - link "Hawking Radiation" - link Another, while heavier and less accessible channel is Physics Explained: link These are closer like lectures, but I enjoy them because they go into the histories of some of these experiments; and what the prevailing wisdom was around the time the experiments were performed: "What is the Ultraviolet Catastrophe?" - this video

Kinda funny. Just before seeing this article I had just finished watching a wonderful video on the "Ultraviolet Catastrophe" ( this video ) which isn't exactly the same as what's being talked about here... but in the same class of problem if you make that class big enough :-). When looking at these sorts of things, surely such "hockey sticks" are often times just not considering the limiting factors? I'm no mathematician (by any approximation) but it seems like more often than not finding such a result should point to some incompleteness or some closer look being required to get the full picture. (P.S. that video was very math heavy and no, I didn't understand most of the math beyond hand-wavy terms... still glad they went into the detail.)