The life expectancy of a website is 3 years.
This story about the parent script of WordPress, b2/Cafelog, built by one Michel Valdrighi in 2001, on Github is quite illuminating. It shows right from the beginning the roots of WordPress (and more so where its technical debt) come from.
PS: You can view the original blog of Michel Valdrighi here: https://cafelog.com/. Don't mind about the SQL error you see on its homepage.