I never imagined my blogs to be useful to anyone. For me, they're mostly just things I felt like sharing but with no particular audience in mind. Over the years though, I find myself receiving email from people who I helped. I even googled quite a few things in the past years only to find the first answer to be a blog of mine. So I unblocked myself a few times.
Blogging is fun. What's obvious for you isn't for everyone.
indeed! this is pretty much exactly how i feel about mine as well. i blog for myself, mostly. i enjoy the act of writing, just about whatever is on my mind at any point in time and inspires me to write about it. i know that i have some readers (like you, i've gotten very kind emails from people who have stopped by my site), and i am very thankful for those readers.
but even if i had zero readers, i would still enjoy the act of writing and putting it out there. i can go back to my blog and look through the years, and see how my outlook on things has changed, how i've grown over time. and the process of writing itself is just cathartic, at the same time.
and as you mentioned, it's fun! :)