This question can also be asked in a much broader scope, why post it at all (Steemit is just my platform!)?
Imagine you get a project at work and your boss will review your development whether it be code or some presentations etc.
You behave differently
When someone reviews your work you put a lot of energy and time, because you are responsible and accountable (maybe you also love compliments).
Now, when you start your own project, the only person you have to present it to is yourself and the users at the end.
Therefore sharing it with your friends and potential user is key to have feedback - lean project management!
User perspective
Potential users that have the anonymity of the internet are more and brutally honest with you. This may hurt when you start out, but it can save you from losing hours or potentially weeks of work.
Imagine you create something and publish it, but none cares and everyone hates what you developed. This is fine as long as you had fun, but what if early feedback could have helped you create something people want?
That's why publishing and sharing your development can bring you the user perspective supporting your development.
Boss perspective
As I already mentioned, having a boss reviewing your work, makes most people keep a certain discipline.
Now, you are the boss of your own project!
To increase your own discipline, publishing and sharing your own work and developments lead to internal discipline. Even if noone follows your project, you think about the entire storyline of your work, are honest to yourself as well as your audience and enjoy celebrating your successes more.
These are the two key reasons why I started sharing projects of mine! :)