Look at the original DB series, the adventures were great and all cast members could jump in to aid Goku on his fights, nobody felt so dragged behind, and then after we learned of Goku's alien origin his race became the number one thing the franchise focused on and talked about ("you aren't a Sayian? Take a nosedive"), Namek-Frieza sagas were more than enough to dedicate to the sayian race whose best warriors' power levels were even leagues lower than Cui's. SSJ sells toys, okey and? Nothing more. Dragon Ball GT was the result of this stupid over-hyping, everywhere in the universe people (sometimes stronger than Majin Buu) were afraid of Saiyans who despite being crushed by first form Frieza were held with the title "strongest race in the universe", not even Uub was important enough to be casted to the front of that show and DB Super was 2/3 of the time "the Goku and Vegeta show", why you ask? "cause Sayians". That's why. Even Beerus and by proxy Whis and all other new deities exist to serve the lore of the "Super Sayian God" who's not even a deity but in fact a normal space impish warrior from a backwater race with good heart (rare among those weaklings) who absorbed 5 other good Sayians' energy.
Dragon Ball has always been the Goku show. He's the main character. Very few people care about Vegeta or whoever, and they always give off the vibe of being contrarians, only supporting the underdogs because everyone else prefers the main guys.