I'm sure many if not most of you who currently are engaged in writing poetey have at some point thought about this question. Actually, it can be applied to any writing. Yes, including blogging.
Perhaps the question as it applies to poetry and blogging are very similar. Unlike novels and other more extensive written works, the market for poetry is much more limited. I've heard it argued, poetry is the most pure literary work, because the author's motives are seldom driven by money and fame. I'm not sure that purity is the proper value here, but I can accept the concept of its special or unique place in literature. Of course this almost screams for an answer to the question at hand. "Who are we writing for?"
Can we agree that poetry, like blogging is often written with no clear idea who if anyone is going to read the finished work? The cultural similarities are perhaps not totally parallel, still, they are a reasonably close match.
Do we write these to satisfy ourselves? How much is ego a factor in our motivations? Do we need a stage in life to perform on... the printed page and the online blog providing that outlet?
I'm not certain that I have totally satisfied my own responses to these questions... in fact I think this is more of a starting place for my own formulation. Something to sleep on... speaking of which it is now Sunday morning. Good Nite.