For me the growth is terribly slow. I wonder whether (1) how long it took you to get > 100 people subscribed and (2) wether you think it's likely to build a general software engineering blog these days
It's taken me several years but is worth it. It goes in fits and starts though. You get popular content and can see 100 in one day where that took several months before. So, I'd focus on creating quality content and the list will mostly take care of itself.