Because we stopped viewing programming as engineering.

It began in the late 90s, with the celebration of "cowboy" programmers like Shawn Fanning - people who created apps that went viral.

But apps created like that always need to be re-written, because they tend to scale poorly, have bugs, and are not maintainable.

Here is one such case: https://www.zdnet.com/article/python-programming-language-creator-retires-saying-its-been-an-amazing-ride/