Why do DJs wait a long time before releasing the track?

I'm wondering why do DJs wait so long before they officialy release the track to the public?

Examples:
David Guetta's ID at DJ Top 100 awards... that was 7 months ago, there's still not much known about the song, nor the release date
Arty's ID at Pier 94 (New Year) - 4 months ago
Avicii & Nicky Romero - Nicktim... It has been out there for 4-5 months, I think, release date is still unknown
Also, Avicii - Silhouettes was released 2 weeks ago, while the song was first played live more then a year ago, the similar case was with Levels, it was played live 7-8 months before release


I would understand if they would play it maybe 2-3 months before release, so they give some exclusive to people at the clubs, and also to see how crowd reacts, maybe make some changes to the track. But why do they have to wait for half a year or even more?

Not all of them doing changes only 2-3 months. As an example, Eric Prydz is working on the most of his music much more than a year.

But actually everyone may have their own reasons. Some of them are searching for the best label to release their stuff, some wanna make their new bangers big enough before the release to get easily in the beatport top, some of them just love teasing, what is obviously the most annoying. Sometimes an artist want his track to become a 'summer anthem', so obviously he will wait for summer to release it. Often happens, that it takes a lot of time to solve all problems connected with copyrights (when trying to release a new official remix, versus & etc..). And ofc, a lot of tracks are getting release just before a new top 100 djmag poll to remind us whom we should vote for. That's how i see it.