This is my first post in any forum and I hope that I help. I have been searching this question in several forums and I can pretty much say that I saw answers that made me sick. There is that habit of people to judge without taking in the consideration the background of what they judge. They hurry to criticize without knowing anything. So listen, when you are about to write on a forum, consult the faq paragraph of the website you are about to call illegal.
For the purposes of this answer I will use https://www.keycardgen.com as a reference, while I will be quoting things from that website. It clearly says on the section called “FAQs” that: “When we say Valid credit card number we are simply saying that the credit card number generated are valid ones because they follow all the rule formula to acquire a credit card number”. You may ask what does that mean. It means that by valid it means that it could be used in a credit card and be considered valid. It also says: “The name, address, expiration date, credit limit and etc. are completely random details which do not hold any real value.” What does that mean? It means that: the card number belongs to nobody.
In such forums everyone suddenly became smart. I saw an answer like “FAKE=ILLEGAL so don’t do it!” Hey you! wake up it is 2019 such websites would be down like by years. It is not that easy to steal money. Furthermore, it says: “All the provided details are do not hold any real value.” Finally, in the question “Can I buy something with this?” the website clearly answers “No! Credit card generated do not hold any real value. They are completely made up and random. Unless you are using it for verification purposes then it could be used for that. Otherwise, it’s a big no.” Those things with the exact same meaning just a bit changed are displayed through many credit-card-number-generators.