Shift your focus. You're not writing for others (strictly) but for yourself. Express your ideas, thoughts, what you've learned. I write a lot, but don't publish, and it's for that purpose. The act of writing is an act of communication, which forces you to formulate your ideas into more coherent forms (and to try and remove ambiguity). If you've just learned a topic, or are learning it, and want to write about it, it makes you think about how to express what you've read or studied (ideally try to do it from memory versus pulling up the references you've been studying).

It's similar to the benefit of teaching, my classmates and I always learned more (in undergrad) by teaching each other in a quasi-seminar format in the computer lab during our study sessions. Someone would naturally take over after a bit as the "teacher" for the session as they found that communicating what we were studying to the rest of us clarified their ideas. Blogging can be similar.