It`s stupid that they make lenses that doesent fit on a 1D serie. I want a 10-20 zoom. But it is only for 1,6 crop kamera. Canon is here forcing me to use a Sigma lens like 12-24 instead of providing a quality wide zoom to use on a 1D camera
Well, I think there are technical reasons and marketing reasons. They needed something to sell to their crop sensor customers that provides the wide angle that is lost due the sensor size. And they needed it on the cheap. From a marketing standpoint it comes in handy that those cheap(er) but relatively good lenses don't fit the full frame bodies, because they want you to buy the very good and expensive specialty lenses in the EF lineup.
And my guess is that in order to prevent people from buying third-party lenses they introduced kind of the mid range lenses that are optically pretty good but slower like the 17-40L.
And for everything wider than 16 or 17 they have a wide variety of primes primes and now even the new 8-15. I mean, seriously, there are maybe a few things that I would like Canon to do differently, but it's really not fair to complain about their lens line up. There is something for every purpose and budget - and still at a better price point than what the other company has to offer, while the quality is traditionally as good or better.