You are likely correct in your thought about them being previously caught in a cage. After they get caught once,, they become VERY cautious about entering another one.
It takes work to overcome their fears.
First off, using a humane cage trap,, with just ONE trap door is required.
Next,, a piece of heavy cloth (towels etc,) need to be placed on the bottom of the cage. (Walking on the wire alerts them.)
Open the trap door AND wire it open to where it will NOT trip. (I'd use zip ties.)
Cover the cage sides & top loosely with cloth or even small brush. Leave the back exposed so they can see "through" it.
Start by baiting it just outside the door. After several days of them being able to eat at the opening,, you move it a few inches towards the inside. get them accustomed the the food without any fear of the trap. Again, slow movement towards the back of the trap with the food will get them used to a good meal, & not getting caught.
Once they are very casual & comfortable entering the trap w/o the fear of getting caught,, then you can plan on actually trapping them. Once you are SURE they are comfortable entering the trap,, then you can actually set the trap to capture them.
Once you catch them, cover the ends to allow them to settle down. Be VERY, VERY careful in all this heat. Do not allow them to stay in the trap for very long at all. Water is critical.