Because there is a large group of "early adopters".
These people love to go digging around in the territory, and many apps get discovered that would otherwise be ignored.
These people also love to evangelize apps strongly, to each other and to the general public, because it gives them social status.
They are a key pathway to an app becoming adopted by the majority - a much larger, much more entrenched group, promising much more profit - and they are very active right now.
Think about any other product space, even the very large and common ones, like shoes, cars, jewelry, sporting equipment, movies, music.
Apps on portable devices currently outpace all of them in terms of the attention people are paying, combined with the upside to being a “winner” in that space.
If your app is wildly successful, you can make billions of dollars.
And so, people like Kim Kardashian feel a need to have computer programmers on their payroll.
Can't say I mind. I'll gladly sell the most expensive very highest quality picks and shovels to anyone who thinks there's gold in "them thar hills".