I don't think there is one answer to this.
I believe my mum is EA to my dad. She is incredibly insecure. This goes back to her father who was EA until the day he died. He loved playing his dds off against each other.
My mum has a history of mental health problems which, in my opinion, is a direct result of her father.
Her EA is subtle manipulation. She was brought up to use manipulation to get her own way and to 'win'. Even Grandads funeral ended up being B a contest of who got to do what job, who was right about the flowers etc.
She doesn't do it with me or dbro as much because we completely disengage. We had words the other week and she started 'I didn't realise I was such a shit mum' , I told her straight I wasn't listening to that manipulation and ended the conversation.
My dad adores her and understands her mental health isn't the best and wouldn't leave her. But he has had to become stricter over the manipulation.
Some people here may say I am EA. if me and dh have words, I need space. I am not sulking, but it takes time for me to process, calm down and deal with my own feelings. Dh wants to talk it through immediately. It did cause issues at first. But now he understands that sometimes I need space. I also understand he needs to talk. So he gives me my space then we talk it through.
I genuinely don't believe me needing space is EA. Dh doesn't either and maybe that's the bit that's important.
I think when it comes to EA, there are many reasons. Some people were brought up in a way that makes them unaware this isn't ok and isn't normal behaviour. Some people are just so selfish as long as they get the outcome they want everything else and everyone else don't matter. Some people want complete control, maybe other relationships have gone horribly wrong and they feel if they had control this relationship will be fine. Some people enjoy having control over others, it makes them feel powerful.
But at the end of the day, people don't want to admit it or accept what they are doing is wrong because then they have to admit they are in the wrong and deal with the fall out from that.