It's a good question. Clearly, I am writing now but this isn't what I should be writing, oh no. What I should be writing is what I'm calling The Book. I should also play the guitar more but that's for another discussion in another time in another place.

Let's rephrase the original question to see if that helps: writing, why am I not? Ah, that's much clearer. I think I know the answer. Let's turn to Steven Pressfield and a quote from his book The War of Art:

The more scared we are of a work or calling, the more sure we can be that we have to do it.

This fear leads to an inability to make progress. Pressfield calls it resistance and says:

the more fear we feel about a specific enterprise, the more certain we can be that that enterprise is important to us

This describes exactly what I'm doing or, rather, what I'm not doing. I think it's time I got over myself and got stuck in.