For me, the #1 reason I don't blog more, especially about tech topics, is that they take too long. Maybe you can bang out a useful blog post in 20 minutes. For me it's more like 4 to 8 hours.

I have to make samples. Since I do mostly web tech I want the samples to actually work, no "here's some code, trust me". I also need diagrams. And, I have to proofread since I'm terrible at getting it right in one or even 5 checks. I write once, add samples, write some more, add images, write some more. Every time I write I add errors, so it always takes multiple passes.