Stop being dense OP. Let me present to you the actual descriptions and some critical thinking.
Caitlyn:
"Headshot
Every few basic attacks, or against a target she has trapped or netted, Caitlyn will fire a headshot dealing bonus damage that scales with her critical strike chance. On trapped or netted targets, Caitlyn's Headshot attack range is doubled."
"Yordle Snap Trap
Cost: 20 Mana
Range: 800
Caitlyn sets a trap to find sneaky yordles. When sprung, the trap reveals and immobilizes the enemy champion for 1.5 seconds.
Sets traps that an enemy Champion can spring, immobilizing them for 2 seconds and revealing them for a short duration.Traps last for 90 seconds. 3/3/4/4/5 traps may be active at once.Trapped enemies take an additional 30/70/110/150/190 (+0) increased damage from Headshot."
Morgana:
"Black Shield
Cost: 50 Mana
Range: 800
Places a protective barrier around an allied champion, absorbing magical damage and disables until penetrated or the shield dissipates.
Shields an allied Champion for 5 seconds. The shield absorbs 70/140/210/280/350 (+70% Ability Power) magic damage and prevents disables until it breaks."
No where in Caitlyn's description does it say they need to be immobolized to be trapped. It simply says that enemy champions spring the trap. So while Morgana's black shield stops the immobilization (since it's the only "disable" thats part of the trap) it doesn't stop everything else from happening. It's a similar interaction to Thresh's Q with the black shield. Thresh's Q "binds an enemy in chains" and also stuns them. The binded chains are not contingent on the target being stunned. Since the binded chains are not an immobilizong effect, they still happen, which is why he stays tethered to a target that has a black shield.
Also, trapped doesn't directly mean "physically immobolized". For instance, you can be trapped in a marriage if your spouse refuses to sign the divorce papers, so there goes that argument too.
And it clearly says in the description it reveals the target, so idk what you're even getting at.