Why does 끝내 주다 mean "wonderful" or "fantastic"?

My Korean-English dictionary, Donga's Prime (1998), says that 끝내다 means to end, to finish, or to complete. It does not have a listing for 끝내 주다, but Naver' Korean-English Dictionary says HERE that 끝내 주다 is an informal expression that means wonderful, great, fantastic, or super and gives the following example sentences:

• 맥주 맛이 끝내 준다.
  The beer tastes great.
• 끝내 주는 영화였다.
  The movie was great [sensational].
• 끝내 주는 아이디어군!
  What a wonderful [super, fantastic] idea! 
• 끝내 주는 콘서트였다.
  The concert was a blast.
• 내가 이 근처에 끝내 주는 스파게티집을 하나 알고 있다.
  I know a spaghetti place around here that is simply out of this world.

First, notice in the above examples that the subjects of the verb 끝내 주다 are things, not people. 끝내 주다 is a transitive verb that literally means to finish and give, so you need someone or something that can finish and give something. A beer can give you a headache, but it cannot finish anything, can it? A movie can end, but it does not normally end something. For example, you can say, "The movie ended" (영화가 끝났다), but what can a movie end (영화가 **을/를 끝냈다)?

As I mentioned, 끝내다 is a transitive verb, so it needs a direct object to form a sentence. However, there are no direct objects that 끝내다 can act upon in the above examples, so the sentences are ungrammatical. In the above examples, 끝내다 is being used like the intransitive verb 끝나다, which does not need a direct object. For example, "맥주 맛이 끝났다" would be a grammatical sentence since 끝나다 is an intransitive verb and only needs the subject (맥주 맛이) to form a sentence. Sure, the sentence, "The beer taste ended," is awkward, but at least it is grammatical. 

Second, notice that all the above example sentences are in the present tense (i.e. 끝내준다 / 끝내주는), which means they would be translated as "is/are ending." So, even if you changed the verb 끝내 주는 영화 (the movie that [one] is ending) to 끝나는 영화 (the movie that is ending), it would still not make sense with the past tense ending 였다 since it would be like saying "the movie that is ending yesterday."

My point is that when 끝내 주다 is used to mean wonderful or fantastic, it is being used in an ungrammatical way. Koreans seem to be using it in a way similar to how some Americans use "He is killing it" to mean he is doing something extremely well, except that instead if saying, "He is killing it," Koreans are essentially saying instead, "It is killing."

My Korean-Korean dictionary does give the following definition for 끝내다:

"운동 경기나 투기 따위에서, 완전히 승부의 마무리을 짓다"

"to clearly decide the outcome in something like a sporting event or competition"

Here is the example sentence given in my dictionary.

마지막 한 골로 시합을 끝내 주고 말았다. 

With the last goal, [I/he/she/they] ended up ending the match. 

The example sentence from my dictionary is a good, grammatical sentence because 끝내 주다 is used in the sentence with an object, the match (시합을). The sentence implies that either I, he, she, or they ended the match with a victory.

Even though the sentence "일을 끝내 줬다" literally only translates as "[I/he/she/they] finished the job," the implication is that the person or persons did a "great" job. Again, notice that 일을 끝내 줬다 has an object (i.e. 일을) and is used in the past tense, so it is a good, grammatical sentence, unlike the way many younger Koreans are using 끝내 주다 these days. Even if younger Koreans know or were to learn that expressions like 맥주 맛이 끝내 준다 are ungrammatical, I suspect that most of them would still keep using them, but I also suspect many older Koreans cringe, at least a little, every time they hear such expressions.