Especially from a storytelling perspective.

Look at "Straight Outta Compton." It mostly focused on three members of ostensibly a five to six person group. It ran two and a half hours, covered about a decade, and there were still complaints all the shit they left out.

Now, imagine doing a Wu-Tang movie: how do you divide up a screen-time/story-telling space for a group of 9 dudes (10 if you count Cappadonna)? They would probably have to make choices and decide to focus on, say, four of the clan members. Which four get the most screen time? Certainly RZA, because he's the acknowledged architect. Certainly ODB, because he's the group's tragic figure. Then who? GZA, because he was basically the first of the crew into the biz? Method Man, because he was the crew's first commercial star? Rae, because he had the group's most critically acclaimed solo album? Ghost, because his, um, "activities" help in their early years and who held them down throughout the '00s?

If you wanted to do a comprehensive Wu history, there's too many stories to tell and a limited amount of time to tell them. If someone wanted to go that route, narrowing the focus to specific era or event would be a good way to go. And, yes, a movie about ODB's relationship with his manager after he got out of prison would suck.