Unlike many, I have the perception that chickens are smart. Obviously, like in humans, there are some smarter than others!! I have two birds in my flock, who come and sit on my lap, even when they know I don't have any treats. Others don't, or come only to check me out. Both enjoy petting and even "ask" for it, in their own way. When I let them free-range in the veggie garden, they spend quite a lot of time just following me around, watching what I am doing. They know perfectly well that stones, watering cans and hoes are not food! Lol... I feel they simply like being close to me. The smartest and most curious birds are usually the friendliest, or so it is in my coop...
Another interesting case is that of my Silkie hen, who doesn't like to be grabbed but makes daily exceptions to the rule, every time she finds an obstacle she can't overcome alone. For example, to reach her favorite spot on the perch at night, she calls me. To reach a particularly high leaf she wants to peck on, she calls me, etc. I have the impression that she actually developed a specific vocalization just for this purpose, because she never makes it for anything else. In these situations, she will make the sound; if I ignore her, she will come to me and make the sound louder; if I still ignore her, she will continue making the sound and start walking back and forth between me and the obstacle; when I finally grab her, she lets me.
My advice for you is to keep the routine, feed them by hand, never make sudden moves, pet them when you can, hold them at least once a day (even if you have to catch them: do it very calmly, but do it). Even the most shy will be calm at sundown, when they go on the perches, so use that moment to touch them. In time, you will know which ones enjoy it.
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