The fundamental reason was that the old bird was ready to end in the Frieza chapter when it was painted, so I didn't think about it so much at that time, and I just put Frieza in the Graman.
If you don't have a reasonable reason, you can actually make it up.
1. This cosmic emperor is only his self-appointed and not widely recognized.
Ephriza, he claims to be the emperor of the universe, but the worldview of the Dragon Ball, the universe and the real universe should be about the same size, a little understanding of astronomy to know, not to mention the rule of the universe, the level of technology required to rule the galaxy, are not high, and the level of technology shown by the Frieza Legion in the comics is obviously not enough to rule the galaxy, at least Vegeta to come to Earth for a year.
Let's say that there is not even a wormhole shuttle, and what cosmic emperor is it?
2. People of higher combat strength levels have other pursuits, retreat, and are not the emperors of the universe.
The daily work of the Frieza Legion set in the comics is to capture the planet and then sell it - you Frieza are the emperors of the universe, and you are still engaged in robber trading? The forced block is a bit strong, right?
And Frieza is so bullish, what do you want to buy?
So Frieza may actually have a bit of a problem with her brain.
The existence of a higher combat power than him, who is okay and still plays the game of "Cosmic Emperor"? The stalls are too big to provoke a protagonist like Goku and then pounce on the street.
3. Buou's prestige was not widely circulated.
Buu's opponents at that time were all at a level like the Southern Realm King God, and Frieza was not yet able to reach it. A low-level one, a mouthful of grass will not grow, and there will be no living mouth, so although Buou is very strong, strength and fame are two different things. And the universe is so big that dozens of dead planets won't be noticed at all, so Frieza doesn't know that Buo is normal.
As far as the new setting is concerned, at least within the scope of the Frieza Army, the existence of the "Demon Buu" is known.
However, from this statement, Frieza called the demon Buu and the destruction god Birus together, and this shows a problem - such as the Super Saiyan and the demon Buo, who are stronger than Frieza, are all just "legends". And it should be noted that the legend of the Demon Buo is much more outrageous than that of the Super Saiyans, in contrast: The Super Saiyans are the strongest warriors born in a thousand years. The Demon Buu was a mythical creature that no one had seen in millions of years, killing four of the five Creator Gods.
To be reasonable, the more reliable "Super Saiyans" have been boring legends and stories that even the Saiyans themselves find boring, and the more outrageous "Legend of the Demon Buo" is obviously less likely to be believed.
In addition to these two, artificial humans are artificial life forms, Sharu is the product of future technology, and Dapra is a person from another world, and indeed they are not the original life of the main universe.
In this way, Frieza as the "Emperor of the Universe" lives up to its name. For a long time, there were indeed no creatures stronger than Frieza in the main universe.