Probably because it is one of the "lower" priced L lenses, and it probably doesn't sell as well as other lower priced L's. Also, it has a nice range to it.
With improved ISO performance and a similar resolution you could argue the 24-105 makes a better all rounder for the Mk3 than it did for the Mk2. With the increase in price(and I'd guess performance) the 24-70 mk2 has become a more speicalized lens aswell not really suited to a kit deal.
I think the answer might be simpler.
Before they release the 24-70 II as a Kit, they want Pros to pay the full price.
With a Kit they would have to provide a little discount already on a lense they just released.
I think we'll see a 5D MarkIII Kit with the new 24-70 later...
I suspect they'd want their camera to shine in the hands of a consumer, and an IS lens is likely to do that more. Plus the 24-70 2.8 is WAY more expensive and people wouldn't understand that it was worth it.
It probably sells better than most lenses due to it's price and range and quality... Having the new 24-70 II kit price would probably scare too many potential ef-s customers away who would otherwise want to move to FF but would need a standard general purpose lens as well, and they have a good thing going with the 24-105... It's widely popular with most photographers and if it aint broke, dont fix it.
I dont think I have missed any other L zooms out here. So the choice is pretty obvious. The 70-200 are too telephoto. The wide angles are too wide.
that leaves you with 24-70 MKII which has just been released and cost just as much as the camera itself. The 24-105 provides a good range. For rich noob photographers who buys the FF cameras, they value zoom more than aperture. And for pro photograhers, it is more likely they will just buy the body and ahve already the lenses they need.
You missed quite a few, but your point still stands.
The 24-105/4L is the the best general purpose L zoom that currently exists. If you only have one lens, barring very specific requirements, that should be it. Hence, kit lens.
Because 24-70/2.8 mk2 isn't really a "kit" lens. It's the top-of-the-line This gives an upgrade path. Just like 17-55/2.8 IS isn't a kit lens with crop gear. Not everyone needs a 24-70/2.8. Some folks are well served with a slower zoom plus primes.
I suppose they could have offered 28-135 IS. It's cheaper and has more range. But they didn't with the 5D1 and 5D2, so why do it now.
In a way it would have made more sense for Canon to have had this lens as a kit with the 5D1 and 5D2, rather than the 40D and 50D which was quite an odd fit. But they didn't. I suppose they figured (rightly so) that the 5D needs a better lens.
It's probably the best way for them to sell a lot of those and customers obviously see it as great value - and rightly so. Had it not been the the kit lens I wouldn't have bought it but for the price as a kit it was hard to say no.
People who then want or need a faster lens will still buy one. Despite having the 24-105 I'm still tempted to get the (original) 24-70. There are good reasons to own either or even both.
If you want the 5DIII with the new 24-70 I'm sure you can still negotiate a good discount once they have been on the market for a little while.
The 24-105 is a workhorse lens, very good quality, reasonably light and compact has great versitility and as others have said is probably the best General purpose lens. the 28-300L is possibly better but its 3 times the size and 2 and a half times the price
The 24-105mmL is a ideal lens for the 5D series bodies. No other manufacturer includes a lens this good as a kit lens. They also discount it a bit. I find it the ideal walk-around lens, I have more expensive lenses, but for general use, the 24-105mm L stays on my 5D MK II.
Comparing its IQ, its price and its IS, what else is there?
I've had a 24-105 for some years and it is the lens I most often use.
While it's only F4, the IS is good for 3 stops, so it would be as good as a 24-105 F2, without IS.
Have you ever used a 24-105?
Try one, you'll fall in love with it.
The colours and contrast are excellent, and it's very sharp too.
Because it has been around for so long, and sells in such big numbers, Canon can afford to sell them cheaply, as the design, development and tooling were paid off years ago, which makes them a real bargain!
What all the rest said about the 24-105. Only downside to it is (in a very dusty environment such as Burning Man) that it extends and contracts when you zoom, unlike the 70-200. Thus, you can air (and dust!) being sucked in and then pushed out. My only real complaint about it, although I would LOVE to have this at f/2.8, but then it'd probably cost as much more more than the new 24-70m2, or it'd have to be variable aperture, or something like that.