In third-world nations, plagiarism is not a serious matter even in university, college, research articles or business companies.
In forum globally, Bitcoin talk forum is a most serious forum about plagiarism but unfortunately plagiarism cases nowadays tend to be handled considerably softer than the past especially in 2018 or 2019.
This is true. Nobody even bothers to check the papers in my university back in the days when written homeworks were a common activities. Not sure if other sites like Facebook and Reddit handles plagiarism differently, but surely some subs in Reddit related to writing enforce those kind of rules (cause why not?)
That is because no one is going after those students who plagiarize other works while professors are lazy checking the content for plagiarism. Or most probably the works have references and state the sources of the information written on the homework.
Plagiarism is a serious thing because you can be sued and got jailed or penalized depending on the amount of damage done to the original owner. Now tell me if plagiarism isn't a serious matter why it is punishable by law?