How do you know they feel that way?
Feedback.
And why would they (feel like I'm not respecting their investment in perception/investigation when they fail to find a trap)?
Let's walk it through: Each PC in a group is going to run their PC through a gauntlet as part of a challenge. Each PC is 12th level. Player A has a pure barbarian with no proficiency in perception or investigation - and 8s in Int and Wis. Player B has a Monk PC with an 18 Wisdom, 12 Intelligence and no proficiency in Perception or Investigation. Player Player C has a Rogue with 14 Intelligence and Wisdom, Expertise in Perception and Investigation, and the 2014 version of Observant.
By the time I design the challenge, I know that these will be the PCs and roughly what their abilities are.
Let's say I decide to put a trap into the challenge.
Version A: The nuisance trap: We have a standard DC 13 to find trap that deals 6d6 damage. DC 13 Dex Save for half.
The Barby won't find it passively, and is more likely than not to miss it even if intentionally looking for it. They'll take a little damage and move on. Kind of boring. Monk has a passive 14 perception, so they might notice it ... or DC 11 passive Investigation so might not. It depends upon whether the DM decides to require passive investigation or perception. That means the DM is inherently deciding if the monk automatically finds it. If the DM says figuring out the trap required an investigation roll due to the design - not just perception - that monk player will have that nagging feeling the DM just decided to have them fail. It is human nature. We may overcome that feeling, but it occurs to all of us (and it is ok to have it - let's not have the people claiming they don't have the same base impulses that we all have today, ok?). Finally, the rogue inherent finds it due to their investment in perception and investigation as they have a 25 passive in each. He inherently can avoid the trap with no investment - which is proper given that he actively invested in choices that serve him well.
Version B: The heavy hitting trap. We have a DC 26 to find trap that deals 20d6 damage with a DC 26 Dex save for half. Barby has no chance to find and may get lucky with those Barby reflexes ... but is going to take a big hit, even if he looks for the trap. The Monk can't find it. They didn't invest heavily in being able to find traps ... so that is an ok result. They might avoid the damage with evasion ... if they get a good save. That could be a good moment. However, the Rogue ... he is going to think he should not bother looking for traps because he has a passive 25. He expects to just find things as he devoted so much to it. Most PCs with Observant 2014 do / did not search intentionally in my experience. Even if he did, he needs to roll a 16 - a 1 in 4 chance - to find it. Again, human nature dictates that the player will have that nagging feeling that I intentionally decided to make them miss the trap ... but here it feels worse as they put so many resources into being able to find traps.
This feeling can be avoided if the players know the DM did not set the challenges. If you're playing a stock dungeon from an adventure path the players are less prone to that feeling ... but it is still there. I've seen it and felt it too many times.
Both Version A and Version B have big problems.
How is this different than combat challenges? Combat is more dynamic than a trap. When a player casts a fireball, the timing (this round or next?), the location (do I get 3 extra enemies by including an ally?) and the byproduct damage (will the fires it sets cause problems for us?) all matter. When a melee character engages an enemy they need to consider their positioning, which target to engage, and how much abuse they can take before falling. Healers need to decide whether to bring up a downed ally, make another ally less likely to fall, or decide that offense is the best defense.
Traps, on the other hand, usually break down to a maximum of three rolls: Detection, disarming/bypassing, enduring (saves). You can liven them up ... but unless your trap summons monsters, they have a huge tendency to be less dynamic than combat encounters.
It is better to not spend the time and effort for detailed traps after a certain point for the reasons above.
But, you ask, what about the PC that invested in Observant 2014? Won't they feel like their investment was wasted if they never encounter traps? Yes - they would. But if you make it clear that their ability is allowing them to find traps and avoid them with quick comments rather than prolonged rolls, you respect the investment without bogging down the game. A few quick comments acknowledging that it made sense for a trap to be there based upon story reasons, but that the PC found and avoided it as it was trivially easy for them to find works.