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.
Basically, tl;dr/TLDR stands for Too Long; Didn't Read/Too Long Didn't Read (you can use or take away the semicolon). Sometimes tl;dr can stand for Too Lazy; Didn't Read, but is mostly the first example.
The most common use for this common phrase as an author is explained in a Howtogeek.com article:
Along this same line, writers sometimes include a TLDR at the top or bottom of their web article, email, or text message. This is meant to be a summary of what the author is saying, and it’s a disclaimer that the details of a long text may not be worth every reader’s time. A ten paragraph product review for a crappy laptop, for example, could simply start with “TLDR: this laptop sucks.” That’s the quick summary, and you can read further for details.
So where should you put tl;dr in your article? Well, it depends; there are pros and cons to using this phrase at either the beginning of the text or at the bottom. Howtogeek.com also describes this:
When using TLDR as an author, your job is a little more complicated. Placing a TLDR-summary at the beginning of an article or email can save the reader’s time or serve as a quick introduction, but it can also give the reader a reason to skip the details of your text.
A TLDR-summary at the end of a long text is sometimes more desirable, as it allows you to sum up all of the details that the reader is digesting. But in some situations, this use can feel a bit sarcastic. It’s as if the author is acknowledging that their own wall of text can adequately be understood in a single sentence.
So really it depends on what your writing, what your style is, and how you want to sound.