I know GT is not canon .. but still it was written by professional writers who wanted to keep earning a pay check lol.. My question is.

Why did Trunks/Goten never fuse? In DBZ Trunks/Goten who could only go SSJ 1 (still a huge feat for them, I think Goten was 7 and Trunks was 9 ) fused and had the power to go SSJ 3 - in terms of power SSJ3 isn't even comparable to SSJ1.

Now in GT they SHOULD be stronger then what they are - at the end of DBZ after 10 YEARS of training Goku wanted Goten to fight Majin Bu in the tournament so at age 17 he was strong as one of the strongest villains ever in DB history. Trunks also had been training with Vegeta in the gravity chamber if I remember correctly.

But say they got weak and can only go to SSJ 2 in GT (which makes no sense, if Goten could match with Bu he would need to be stronger then SSJ 2) why couldn't they fuse and be effective?