Super Saiyan 3 appeared to leave all the warriors speechless. Dragon Ball Z and those of us who grew up watching the series in the 90s. Goku achieves this mode after his training in the afterlife, after having died in the fight against Cell.
The protagonist of the series goes down to Earth for a day to visit his friends and family, and unfortunately it coincides with one of the greatest chaos that the Z Fighters have faced: the threats of Majin Buu.
By then, we knew that Goku did not do it because, being dead, he could not consume as much energy and shortened his stay in the world of the living. However, when he returned from the dead we did not see him executing this transformation, with some exceptions.
Why didn’t he become Super Saiyan 3? This transformation was far superior to that of Gohan’s Super Saiyan 2, but the reality is that, according to Goku himself, it consumed too much energy during a fight. So, if the opponent was at similar power levels, being in this mode was going to make him lose due to fatigue.
In this way, for the Saiyans it was not an option to be transformed into Super Saiyan 3. That is why Goku does not use it anymore, we never see Vegeta executing it, nor Gohan reaching it. Everyone decides to go for Ultra Instinct, Ultra Ego or Beast.
The Super Saiyan 3 transformation was only performed by Goku and Gotenks, a fusion of Goten and Trunks.