Contract expirations & group member changes

I'm traveling, so this post is likely to be short, but I just wanted to point out an interesting phenomenon in Kpop, which has actually also happened in American pop culture as well: group member changes (교체). I thought I had posted on this before, but regardless...

Most recently, it was announced that one of Kara's original members Nicole would be leaving the group after her contract expiration.  Also, Jewelry's Eunjung's contract also expired recently so we will see if she will also leave the group. Davichi's contract expired, and it isn't clear what exactly is in their future (although it looks as if they are going to release an album with Core Contents Media despite the contract expiration). Long time soul/ballad singer Gummy moved companies after her contract expired. Finally, after Wonder Girls unofficially didn't-break-up-but-stopped-promotional-activities-due-to-leader-Sunye-got-married-and-had-a-baby (also known as indefinite "hiatus") Sohee left JYP and expressed a desire to start an acting career. Of course, before Sohee, Sunmi left the Wonder Girls and is now a solo singer.

I am sure there are more that I missed, but notice a trend in these group changes

they can be for any number of reasons, but there seems to be a couple that stick out to me

• desire to transition to a solo artist --> this is a difficult transition because groups are considered as safer, and more successful in the music market because fans are likely to at least find one group member they like / are particularly drawn to. You can be inside a group and still have a strong solo musical career (Big Bang would be a perfect example of this). But the awkwardness of this is due to the fact that fans don't want groups to break up. Thus, you are almost kind of stuck with your group even if you want to advance into the solo market because it is seen as abandoning your original/true fans who were there from the beginning. There are some groups (SNSD comes to mind) that claim that they will forever be SNSD first. Whether or not that will be the case, fans  love the idea of their favorite group member going solo, but it appears that they want you to go back to your roots. In short, don't abandon/betray your group. 
• desire to transition to an actress --> The actress/idol line continues to become blurred, with actor-dols like TOP, majority of CN Blue, Suzy, ect who have done it without giving up their group status. Could Sohee have been able to do this without leaving JYP? It is questionable, since Taecyeon, Suzy, and Junho seemed to make do pretty well. But again, this is a weird conundrum, where certain idols are becoming more and more popular as actors (see: Tiny-G Dohee, rising to fame for 응답하라 Reply 1994). It is a double-edged sword, where in Dohee's case you brought more recognition to her group Tiny-G, but she is really becoming known as an actress, not as a singer. So she continues to have acting opportunities, and the group can't perform without her because she is the most famous group member, but music programs & activities as a singer take up a lot of time so it becomes extremely difficult to do both. 

It will be interesting to see if these stars continue to rise after leaving their groups or if it will become extremely difficult to them to maintain status in the idol-world. Sunmi from the Wonder Girls managed to be pretty successful, and has released 2 singles. But initially, she left Wonder Girls to attend school, and then she came back as a solo artist. What happened to the rest of the Wonder Girls? It seems Yenny is producing and writing more songs, but (at least to me) it's unclear what the other girls are doing. 

Also, I couldn't think of an example in K-pop where this happened to a male group. With the exception of 2pm, who didn't change group members, they just left Jay Park out (who later became a solo artist). But there were plenty of girl groups who have done this previously (i.e. look at T-ara, who manages to add, remove, add, and then remove group members). 

A quick comparison to American popular music? The first example that comes to mind would be Destiny's Child, where two members left, replaced by Michelle Williams, and then of course Beyonce's wildly successful solo career. I couldn't really think of any Korean comparisons to this, since many girl groups tend to people popular for difference reasons (physical appearance/rap ability/vocal ability/ect). 

The male example would be Nysnc, perhaps? Where Justin Timberlake later became a successful solo artist. But again uncertainty about male switches, so if you know of any examples, please feel free to let me know. I am jet-lagged.