That's a difficult one to answer because I can't really think of it as submission. I think of it more as release of your inner self, something that you have, or feel you have to, keep locked inside. It's not an easy thing for a male to admit he wants a female to have power over him, that he wants to be her submissive or her slave.
By its very nature the word "Slave" creates a very negative effect in a lot of people's minds. Chains and shackles and all that kind of stuff. But within the context of BDSM it's a very different thing. But try explaining that to people and it's almost impossible. No matter how liberal or open minded a person is, many of them still cling to the idea of Men are X and Women are y.
The question was why do males submit. Well there are a lot of reasons. One is the mere kink/fantasy one. The male needs to submit for a few moments in order to release pressure that is building up inside, It's pretty common in males who have high powered stressful jobs where they constantly need to create an image of bravado. To be able to be in a position were somebody else has power over them and all they have to worry about is obeying a series commands can be a huge relief. And the fact that they are submitting to a woman makes it even more intoxicating. They feel the loss of power even more intensely.
But this is merely a kink thing. It's important to the individuals concerned but what about a male who seeks a sub/ domme or a mistress/slave relationship? Where does that desire come from. Is it weakness?
A lot of people would think so. They would be repulsed by the idea of a male wearing a collar and kneeling at a woman's feet and wanting to give himself to her, to serve her, to take pain from her. How could this even be defined as a relationship? Where's the love in it?
Well the first thing I'd say to that is a male who seeks this kind of relationship and who reallly wants it doesn't submit to an image or role. He submits to a person and that person has to have qualities that awaken his desire to submit. And no love in it. I don't think there's any better love than being totally accepted for who you are. Acception that is not based on your gender but on you as a person.
I think also that males who have this desire are pychologically stimulated to an extent by feminine power. So what exactly do I mean by feminine power? Well I dont mean a woman who adopts all the characteristics of a cliched male and then tells us that she is striking a blow for feminism. I mean a woman who is totally comfortable within herself and recognises the power that she has.
Where sometimes male dominance can be based on swagger and strength, Female dominance can be very silent. But a part of you feels it. Some males can pick up on that and they respond to it.
That in itself is not enough however. There needs to be more. It takes more than the label "dominant" for a person to want to reveal themselves completely and give themselves completely to another person. At least it does for me.