Why does Siri require me to unlock my iphone when I use the button on the steering wheel to ask siri to read texts or get directions?

I have the switch "Allow Siri When Locked" on my iphone 16 running iOS 18.5 switched on. When I am driving and use the button on the steering wheel of my 2018 Chevy Colorado to ask Siri to play music while the iphone is locked, Siri starts playing music as expected. However, when I use the button on the steering wheel to ask Siri to (1) read texts or (2) get directions, Siri responds: "You'll need to unlock your iphone first" even though "Allow Siri When Locked" is on. Why is this?