Why is it in the end, I see this often after reading the material. The definition is too long, didn't read, but by the time I see the tl;dr, I've already read it. It breaks the flow of the whole story and becomes redundant if the entire article is read. I have no idea why so many writers continue to put it in the end. Its oxymoronic. What is a good reason to put in the end?
It's targetted at people who won't read the thing. Given that you read the thing, you aren't its target audience, so all it needs to do for you is stay out of the way, which putting it at the end does (whereas putting it at the start might lead to you not reading the thing when you otherwise would do, which is a negative for the author).
The target is people who skip past the text without reading, who see a quick summary at the end that they are willing to read.