Sagas was made by a small company called Avalanche, I think that would explain a lot.
As unbiased as I can be, I don't ESF takes anything away from the mainstream gaming market. Compared to the Dragon Ball Z games released for the console, this mod can barely compete with the fanbase (so to speak) of the consoles. Why? Well, the Dragon Ball Z games that were released for consoles and hand-helds have more popularity due to publicity (mainly advertising). Not to mention as each day passes, gamers want better graphics, better gameplay, better stories, which ESF struggles to do since it is limited to an outdated game engine.
I mean no offense to the team or this mod with what I said previously, but I'm just saying there is a higher demand for grade A games than something that looks ancient. Sure ESF is free, it has to be unless the rights were bought to legally add a fee. By my understanding (please correct me if I'm wrong), if the team bought rights to use the likeness, names, etcetera of everything in Dragon Ball Z, then the team would have to charge people to play the game to pay off royalties.
All of that is just what I think, so there is a good chance I'm wrong with what I said, and if I am, I sincerely apologize.