At first they stopped the production from 2000 until 2009, even though the manga is released every week and has already gained a lot of episodes and popularity. Why would they not make more chapters of anime?
Probably the anime wasn't profitable enough to mantain a stable series. Hajime no Ippo's manga sells well, but not overwhelming well despite it's lots of volumes (more than 100, selling way less than big blockbusters like Naruto or One Piece, which have half that amount), so while being popular it isn't a big hit like other series. The old-school graphic aspect may be another issue, that style don't sell well nowadays.