How can One song has so many cover version?!

I was just minding my business surfing Youtube when I came across an old Chinese song called "今生註定" translanted "Destined in this Life". It was sung by Linda Wong and Gao Ming Jun. A nice duet piece, the only thing is that it is a bit short.

Then I remember a Japanese version of this song that I hear some years back. I search in Youtube and guess what I discovered?

This song which is called Sekaiju No Dare Yori Kitto has 8 different cover versions!!

The first which is the original composer Tetsuro Oda sung it. It felt like those80s style ballads and you can imagine yourself walking in the beach while playing it.

WANDS Version
The second is done by WANDS which I love them. (Their Slam Dunk ED2 was one of their best songs) The tempo is more faster like how a rock band WANDS will have perform it.

WANDS and Nakayama Miho Version
But wait, there is another version which is performed by Nakayama Miho and WANDS which actually is pretty good considering this song can be performed as a duet.

Then we have Noriko Sakai Version which is more of an Idol song but with a cheerful beat. I can't really hate Noriko despite having a bad marriage. She also prove that you don't need a more mature performer to sing it.

Fast forward to 2000s, COSMETiC Drama, a techno group did their version which is not bad but short. (They performed it as part of a non-stop megamix.)

Shimatani Hitomi Version
Shimatani Hitomi also performed her version which is really nice and it has her own style.

Finally, if you think only Asian people love this song, Debbie Gibson and Eric Martini did an English version of it and I got to say it is good and it is better than the Chinese version but lose to the WANDS version.

My top three version are:

1) WANDS and Nakayama Miho Version
2) Linda Wong and Gao Ming Jun Version
3) Shimatani Hitomi Version

Why I like this song? Probably it is one of those few songs which both male and female singers are able to perform without going off-key. It is beautiful and the different styles of each version make it good without ruining it.

But still that haven't answer my question?

How the hell can one song has so many cover versions?!