Here is the Wikipedia article about it). There were many contributing factors to the crash of the video game industry at that time, but one of them was a market lacking organization flooded with bad quality titles. How could you tell the difference between a good game and a bad one? In an age before the internet, this was much more difficult to figure out.
Right now, pre-made flashcards suffer similar problems. There are many flashcards available from many sources, but curation is practically nonexistent. Will there be good sets of flashcards out there? Yes. Are there reliably good sources that consistently publish flashcards that adhere to the "20 commandments of knowledge formulation"? Not as easy to find.
Why is this? While Spaced Repetition Software has advanced greatly, public acceptance has not; traditional and archaic learning methods prevail and show no signs of changing due to the global institutional dysfunction (Among many other things). In other words, people don't really care because they don't understand that SRS is superior to traditional learning. Also, the public as a whole has not been taught how to properly structure a flashcard. Thus, many of the flashcards that do exist are poorly constructed.
So while there might be a few good sets of flashcards out there, I've found making my own much easier than modifying poorly formulated pre-made flashcards and weeding out unnecessary ones (Which you will likely have to do). It is also easier to personalize your flashcards (Add pictures, reference memories, etc.) right from the start, thus making them more memorable.