Why were 17 and 18 evil in Trunks' timeline?

[Duo]

In a world where Broli is traumatized by infant weeping, the #17 & #18 parental death scenario makes a whole lot of sense. That idea has a lot more content behind it than just saying "they were more evil for some reason".

(And the internet screamed "non-canon!")

[90sDBZ]

Perhaps the years of having all that power and no-one who can stop them turned them a little strange/unstable.

That still doesn't explain why they'd lose their sense of excitement at fighting a strong opponent. Present 17 liked a the challenge of fighting Piccolo one-on-one. The future Androids had no challenge at all until Gohan so you'd think they'd have more reason to fight one-on-one so they could savour the rare opportunity of a challenge and yet they ganged up on him like cowards.

[ABED]

I know a lot of people want to try to lock down behaviors to some watershed moment, but if 10 people in the same scenarios, they aren't all going to react the same way.

[AvatarReiko]

I think it had something to do with when they were released. When present Gero released 17 and 18, he mentioned that he had problems with them in the past and still needed to work on them. Perhaps, in the future timeline he made them more evil. The present androids were less sadistic and murderous. When 18 was talking to Cell she even implied that 17 was focused on killing goku and loved to mess around but would never take a innocent life. I think it is a combo of future trunks's time travelling and Gero not making them as vicious and murderious