Bulma's wish in the buu saga

[sintzu]

When she asked Shenron to bring back all the people who died back to life why wasn't Vegeta brought back as well ?

[NANLIT]

That was beause Vegeta had already been revived once with the Earth Dragon Balls (when they wished to revive those killed by Freeza).

[mAcChaos]

Alternatively, they said "except the evil ones." Which could include Vegeta. I forget if they had improved the DBs by that point or not yet.

[Darkprince410]

They had upgraded Earth's dragonballs to include multiple wishes by that time (had done so in the Cell Saga) but other than that they still were restricted by the same wish limitations that they had before. They couldn't revive someone that had already died before, even if the wish was different. That's why Goku wasn't revived when a wish was made to revive everyone that had been killed by Cell, and regardless of whether or not he'd have been included due to his alignment, Vegeta wouldn't have been wished back by the wish Bulma made.

[Tyro]

They had upgraded Earth's dragonballs to include multiple wishes by that time (had done so in the Cell Saga)

IIRC Dende upgraded the dragonballs in the Cell arc to grant 3 wishes, but that was limited to 2 if one of the wishes included reviving multiple people. By the Boo arc I think they had been upgraded again to grant 3 regardless.

[Son Edo]

Namek dragon balls were upgraded off screen.