It doesn't feel like the series was axed and even if it was I think it was for the best(although I don't think the series could have gone on more than 4 volumes). The series had one of two options, it would've been either prolonged drama that ends in the last chapter or what we got right now, a good natural ending that completes the story of every individual character, a good ending for a short series. There is no reason to have a series go on for more than it needs to.