There are plenty of electronic components which were once ubiquitous but once the niche which led to their existence has passed, they fade away to remain a junkbox curio. The DIAC is the subject of a recent ElectronicsNotes video, and while it might not quite yet have slid into total obscurity yet it’s definitely not the most common of parts in 2023.
This is a companion discussion topic for the original entry at https://hackaday.com/2024/02/03/why-not-try-a-diac/