Quite frankly, I don't care about small single-purpose apps. The UI on phones and tablets aren't designed to help us find one app among dozens. In most cases, you bump into limitations as soon as you start using it. In many cases, you'll use it a handful of times then never use it again.
If you are looking for anything that is even moderately sophisticated, chances are that no one has made an app for it. There will already be an app in many software categories, but they provide basic functionality at best. Consider what passes for word processors and spreadsheets, or even web browsers and email clients these days.
If you are looking for anything that doesn't lock your data into an unsupported proprietary file format that is hidden in some unfathomable directory on your device, or forces you to use a network service to access your data -- well, good luck. While there are usually options for content consumption, content creation is hit-and-miss.
There are a number of reasons for this, but the biggest one is profitability. Very few people want to make a cheap app that takes a lot of time to develop. A lot of people want to translate the sale of cheap apps into more profitable online services. So what we tend to end up with are a bunch of apps that go after the low hanging fruit and sound revolutionary, when in reality they are little more than toys that you could easily accomplish with a single generic application.