Playing passive is a combination of letting the enemy make an offensive so your team in turn can lead them into a trap and make a counter offensive by blocking off their escape, and gauging their patterns, their strengths, and their weaknesses. At some point, you need to take a stand and push hard at wherever you perceive the enemy's weakness to be, and crush them with one decisive strike. A game isn't won by letting the enemy constantly knock on your front door.
Some champions are better at the passive play than others. Mages and ranged champions in general are better at passive play, being able to safely push back the minion line from a distance by targeting entire crowds at once, but melee fighters and assassins - mostly champions that focus single targets at a time, primarily at close range - are not. You have to be aware of how good your team is at doing this; most players are absolutely incapable of telling the tactical differences between a Yasuo and a Vel'koz.
And that is where people trip up, among many other areas. People mistake passive play with letting the enemy take one objective after another without contest, all without claiming something of equal or greater value. If they take one turret, push to take two. If they go for dragon, go for Baron. If they go for Baron, take their Nexus. You have to know when to let them take an objective, when an objective is lost, and when you're in the perfect position to take advantage of their focus elsewhere. Again, most players are absolutely incapable of understanding glaring differences, let alone nuances. I can't tell you the number of times I've seen people who will drop everything in bot lane to rush towards a contested Baron, not understanding that it would take too long to get there, that the enemy would have killed the Baron, recalled and pushed out the lanes before they even got halfway there. If I'm too far away from a contestable objective, I don't try to double time it over there. I double down on my current objective, instead.
So yeah, it's a tactic just like almost everything else, but people as a whole have the tactical prowess of a gerbil with a concussion, so they use the wrong tactics at the wrong time in the wrong place with the wrong champion against the wrong enemy for the wrong reasons for the wrong objectives.
