I do like how 5e does proficiencies for the most part. I think there should be a few more of them, though. What I don't do at all are passives. I dislike the concept of passives, because a person isn't going to always be average when something important happens.
It's for making things easy to use. You could just as easily argue that having a single, static bonus to AC from armor, shield, Dexterity, etc. makes no sense--characters should be able to fumble a block or accidentally expose a weakness, thus making it easier for the enemy to land a blow.
But, if you need a physical intuition for accepting it, it's literally just Take 10. You use Take 10 when the action can be repeated at least a few times and an average result is reasonable. It may not be the case that every
individual effort is average, but continuous minor efforts will (by the central limit theorem) trend ever closer to the average result. You aren't--or shouldn't be--using passive perception for something the party could only see momentarily. That's what a roll is for.
As for insight, I don't use it very often because I won't let it be a lie detector or a give us a clue skill, and it's useless otherwise. If they use insight and don't pick up on any body language that would give away if the NPC is lying, was that a failed roll or the person was telling the truth? They can't tell, so why use it?
This problem is no different from Perception--yet presumably you still use it as an active skill. Going further than
@Swarmkeeper did with their example, Insight can be useful for achieving not just "clues" but
social understanding. Showing you care, for example, generally requires sensitivity and patience. Delivering an armor-piercing question (or response) in a way that really lands. Calling attention to someone else's behavior in a way that encourages them to change for the better. Etc. Anything that is a non-trivial "show understanding of another person" can be an Insight check, if a check feels warranted.
This is one of the reasons I always made room for Insight on the Paladin characters I would play in 4e. If you're going to commit yourself to drawing out the best in everyone, even your opponents, you need to be able to
see the best in everyone, and to see
how you can draw it out.