Except everyone got their chance, again and again and their arc have been finished for a long while, them getting sidelined is just the normal progression, once there is no more struggle, why would they have the spotlight outside of slice of life episode ? they even addressed Krillin's decades worth of PTSD and Tenshinhan made his school to 'redeem' the crane school, none of the characters have any motivation left beyond survival and you don't need 20 characters who are just there because they'll die otherwise, you might as well reduce the cast.
Also, there is no 'star player' thing, unlike power rangers, the show isn't based around a team, it's based on Goku, he can be solo or with his friends, DB isn't like One Piece, D-Gray Man, Naruto or Fairy Tail, none of the characters are part of an official group, organisation or team, they only showed up before because they wanted to and when they wanted to and the team / organisation is at no point the center nor the framing device of the show.
Hell, the only reason Power Rangers can use that formula is because they can change the whole team whenever they want, they don't just keep doing that with the same characters over and over again.