I've been writing every day for some time now. Be that as it may, I don't have a massive amount of writing done. The bit of text I sent out/posted about my experience of being a kid when the Challenger exploded took a week and a half to write.
Why is this?
When I write, I focus on each sentence, one at a time. I write a sentence, then edit it, sometimes re-write it, put something in, take it out, repeat. I'd stick at it till I had a sentence that I thought was good.
For me, writing good sentences involves lots of reduction. The first draft of a sentence is often too long. I have to run it through a "Write more like Samuel Becket" editing routine. Pretend I'm paid to cut words. Refine the sentence till only what is necessary for it to do what it needs to do is left.
Every sentence should do something and set up the following sentence. Some sentences work together in a group; they make a paragraph. The paragraph should accomplish something more advanced than each sentence. But if each sentence is not good, the paragraph will not be good.
Writing at the sentence level is slow going. (At least it is for me.)