Dragon Ball Super has added several new layers to the famous franchise, all the while bringing back elements and characters that had been somewhat looked over or hadn't been prominent in a while. One of these is Majin Buu. Though he was the final villain in Dragon Ball Z, he wasn't featured very prominently in the now non-canon Dragon Ball GT, making it somewhat easier to forget him. Sadly, Super has knocked him backward as much as it's pushed him forward.
Though Dragon Ball Super brought Buu back into the limelight in a more overtly heroic fashion, it failed to feature him in one of its biggest arcs. Buu's absence during the Tournament of Power was explained in-universe, but it still feels awfully hackneyed. Here's a look at the most likely true reasons for Buu not showing his stuff at the Tournament of Power.
Buu Failed the Written Test to Enter the Tournament of Power
The Tournament of Power in Dragon Ball Super is as grandiose as it sounds and quite deadly in nature. Held between the various universes within the multiverse, the fighters representing each one battle for much more than mere titles. Any team that loses will have their universe destroyed, as the idea behind the tournament is that the Grand Zeno believes there are far too many universes in existence.
Majin Buu was initially part of Universe 7's team, which represents the primary realm of Dragon Ball Super. The arrogant Saiyan prince Vegeta actually questioned this, as Buu was known to be weaker after splitting from his evil incarnation. Goku, however, noted how much incredible power Buu still had, and that he'd be a vital asset to their team. Unfortunately, through failing the written test to enter the tournament as well as falling asleep before a fight, Buu was unable to help protect Universe 7. This forced Goku to recruit Frieza in order to have enough team members.
Why Did Toriyama Drop Buu From the Tournament of Power?
Though the narrative reasons for Buu being absent during the Tournament of Power are plain as day, it still doesn't explain why he was left out after Goku even explained how useful he'd be. Part of it was likely the potential of Goku having to fight on the same team as Frieza -- the slave broker of his species -- in order to protect their universe. This not only provides for some gravitas, but it also helps that Frieza is a much more popular villain than Buu.
It could be argued that Buu was too silly of a character to be able to compete in the serious nature of the Tournament of Power. This is backed up by his falling into a lazy stupor, as well as his not being smart enough to even pass the written part of the entrance. Despite these setbacks, he, as Goku pointed out, was still an incredibly powerful fighter. In fact, the real reason for Buu's being written out of the Tournament of Power is likely that he was too powerful.
The tail end of Dragon Ball Z saw Buu put quite a hurtin' on the powerful Vegeta, and more recently in Super he had trained to gain a more svelte, robust form. Buu also had incredible abilities such as immense stamina, healing other fighters and the power to turn opponents into candy. This logically could have made him too tough for anyone the Tournament of Power would have thrown at him. After all, even Buu would've gotten serious if innocent people like Hercule were threatened, and he was no slouch when it came to using his powers at opportune times. Sadly he was unable to show off his true potential in helping determine the fate of his universe, with Super rendering him a slovenly goofball -- at least for now.
