It appears you give snakes no credit. It sounds like you think they should do what you want.
You forget, these are wild animals and do have a mind and agendas of their own. And they are not all alike.
As a person who has bred kings since 1964, I can tell you, its ALL ABOUT YOU. They always react to you.
I do not want to be racist, but I kind of have too. Some people believe and live by words. Other people believe and live by feelings, you know, the stuff words discribe.
Animals and in particular a voiceless creature like snakes, live by feelings. In fact, their lives depend on that. Think about predator prey relationships where they hang out together for long periods, then all of a sudden the prey knows when the predator is a threat. This is common in the snake world.
So with snakes, you must be secure with yourself and you must be confident and you must be none threatening. If you fear a snake, it will bite you. After all, there is nothing more dangerous then a fearful animal. Of course humans are very complicate so there is much more to it. But its about you.
There are funny behaviors like strike range. With snakes, if you stay away, your fine(of course) or if you move right in and pick the snake up, your fine, but if you stop and hesitate 6 inches from the snake, your dead meat. They will bite you. Its like your a perfect target and to easy to refuse.
Also snakes are individuals just like us. Some are very tolerant, others are not, of course, some are inbetween. But all kings quickly learn to trust you. If you are trustworthy. But if you feel fear or are insecure, you are not trustworthy, that threatens them. How would you like a giant fearful, insecure predator playing with you? I think you would just pee your pants and pass out. hahahahahahahahahaha snakes are much stronger then you.
How would you react being picked up by King kong. My bet is, we would all be afraid, but some of us way more then others. Also, how would you react if king kong had what looked like blood on his lips????? To snakes, you ARE a giant predator.
Doing this is like doing anything else, it requires an education. YOu must go through a learning curve. Also some folks just do not have what it takes, like in any area.
All of us old time herpers know someone who is bitten everytime they pick up a snake and by snakes that don't bite. Also for some reason, this type of person keeps doing it and keeps getting bitten. Again, you cannot blame the snake.
Its always about you and you are the one putting the snake in a cage. Consider, if the snake does not like the cage, and you keep putting it back there. It will not like you. Hmmmmmmmm heck thats the same or cats, or mice.
Again consider, you are huge, they are small, that is offensive enough, most all animals react to size(threat/bluff behaviors) With most animals, the person needs to work or posture, like to not appear large or threatening. Do not make direct eye contact. These and many more are common animal training protacal.
So its you that must learn to create a situation of trust. Good luck and don't look to the snakes to fix this. Cheers