Google's Android does not like external storage, even when it's your internal SD Card - it never has. Possibly out of simplicity, after all, it is much easier to control the file structure in one place, especially when it comes to removing an application - those pesky files all need to be removed for a nice clean uninstall. With a device like a smartphone users are more apt to download, install and then uninstall multiple applications trying to find the one they really want. When you have a PC and pay a lot of money for an application, you make sure that is the one you want before you purchase and install it, however, when an App is free or a couple of bucks, we tend to be a little more free wheeling when it comes to downloads and leaving a bunch of unlinked files could slow up your device.
One solution is to do away with SD Cards altogether - many manufacturers do not include the card slot any longer - the new Moto X and Moto G, for instance, do not even offer it as an option...although we must make note that Google owned them at the time they were released. HTC finally offered one in their HTC One max device, but their flagship HTC One never had one - they claim due to space requirements...maybe HTC does not realize just how small they are. The LG G2 is also lacking an SD Card and is one of the "cons" listed in the reviews, and of course, none of the newest Nexus models have a SD Card slot, again Google controlled. Then there is Samsung, bucking the tradition and offering a SD Card in all of their major devices, although how the SD Card is used, may finally force Samsung to follow Google's guidelines more closely.
The changes made in Android 4.4 KitKat mean those apps, by default will get their own 'private' folder on the SD Card where the app will be allowed to do anything with no permissions required. In other words, these folders will be like the private folders on the main storage, but with little security because the SD Card can, by its very nature, be removed and read by a computer. The third-party apps will still have unrestricted access to the public folders on the main storage, but writing anything outside its designated private folder is strictly off-limits. Google said in their documentation that this was done to ensure "the system can clean up files when applications are uninstalled." The important thing to realize here is that Google is saying that when an application is uninstalled, any information written in its private folder will be erased. So if you have your third-party camera app storing its pictures on the SD Card, you will lose those pictures if you uninstall that camera app. You would have to make sure that you first backed them up outside the SD Card.
This could be a way to push users to store everything to the cloud, but more than likely is to steer OEMs to use a new KitKat feature called Storage Access Framework (SAF) for those of use that do not keep files stored in one place - whether they are stored on the cloud, the phone, or SD Card, the SAF can access them. If the Apps are configured properly, the SAF could allow more than one App access to stored files from one another and modify or delete them - where the data is store would become irrelevant. This SAF could replace the classic file-system access and may have a bright future and in the end we could wind up with a better user experience. However, it may be a little rocky of a road to get to that point, with OEMs and App Developers all on board, so in the meantime, make sure that all of your data files are backup in the cloud or on your laptop or PC.