Why? Because passives are cool.
From silly and unbalanced to seriously balanced ones, let us hear it!
If every hero were to have a passive, or change how some existing ones work, what would you give them?
Ill give you an example:
Reinhardt
German Engineering: Reduces all knock back, freezes, and stuns by 50%
Roadhog
Thick Hide: Hogs thick skin reduces all enemy ult gains by 10%
Reinhardt needs some passive that reduces Crowd Control in some way.
Nice passives. I think some heroes could indeed have one 
Opportunist rework: Sombra can pick up and use weapons from heroes who have died.
Omg. This sounds SO FUN
Sombra with an Hammer 
Nice concept.
20 char
Winston: powered by peanut butter. On death enemies drop jars of peanut butter which will restore 1 hp take 1 second off all cool downs and add 1% ult charge each (also every time he pick one up the OH YEAH voice line plays)
Did someone say Peanut Butter? 
Ana: Sharpshooter - Scoped shots pass through barriers but are halved in effectiveness per barrier
OMG. Do you know how annoying, yet awesome that would be? LOL
Rein seriously needs at least a grounded passive. He gets knocked around too easily
Ana needs a healing and/or mobility passive.
Ana needs a passive that gives her self-sustain or something.
It has to be quite conditional though, like only when he’s only holding the shield up for a certain amount of time. Because the idea of a nano-boosted Rein not being deterred by CC is a bad balance design
Ana /target self /inject dart
Im not saying he just doesn’t get stunned at all, he just needs to have a passive where he cant get stunned as easily
Each headshot reduces 1 second off combat roll’s CD
Ana - (Not sure what to name this passive)
She can now climb walls & Has the option to jump off of them if needed. Think of it kind of like Lucio x Hanzo/Genji passive
Ana: passive “tracking dart”
When Anna hits an enemy their location is revealed for 15 seconds.
What about:
Seasoned Medic: Ana heals herself for 10% of every healing/damage dart landed