Once upon a time it was quite elegant. Then, like everything Facebook acquires, it grew into a bloated "why not?" monster.
There is an ever growing demand for new features, not necessarily from users, to fend off rivals and to stay relevant and exciting. As with a lot of popular apps and services, it ends up bloated, trying to offer everything to everyone and satisfying no one.
Except it didn't, the photo quality on Instagram is really bad because of compression and it is not possible to share actual good pictures because of that.