I've always been curious as to why so many submissive men get aroused by being humiliated. I too get aroused by being humiliated (by women) and it doesn't quite make sense to me.
I know many (but definitely not all) submissive men have often struggled finding relationships at various times in our lives, myself included. It's during those bad times that I've found it common to start analyzing your own inadequacies and flaws in an effort to improve and become a more attractive person.
There are, however, certain weaknesses or flaws that we have that aren't able to be changed. These can be physical, such as your height or penis size, kinks and fetishes that we find shameful (as would most vanilla women), or other personality traits that may stem from trauma or long periods of neglect such as feeling insecure, unlovable or invisible. While it is possible to change some of these things through surgery, medications, or long periods of therapy, many of them can only become less of a problem and won't really go away completely. The emotional states are also much harder to cope with when you are in a down time since it's the down time that is exaggerating those feelings.
I think the fact that even after a sub has found a woman (Dominant or not) that accepts him as he is still reacts with shame and humiliation is a sign that it's very difficult to outgrow many of the emotional scars one picks up over the course of their life.
I think that humiliation is craved by someone who has not found peace in themselves that this is how they are and how they are is okay. e.g. they don't feel like it's okay to dress in women's clothing, they feel their penis is too small, they like being pegged but are embarrassed by it, etc. I guess this is kind of obvious though, since if someone was completely at peace with it, it would no longer be humiliating.
What further complicates things is that subs generally want to be humiliated in a certain way or by a certain target group. A sissy might go on a public outing in order to get noticed by a group of women or girls and laughed at but at the same time, might hate to be noticed/approached by a group of men and find it downright terrible to be noticed by their family. This creates a bit of a separation between being humiliated in front of strangers (with no long-term consequences) and being humiliated in front of people they will see repeatedly. In the fantasy of it all, those they will see repeatedly will "play along" with the situation. Humiliating situations that will have lasting consequences on their daily lives generally have no appeal to subs.
What is odd is that the group (whether they be strangers or people they know) most subs wish to be humiliated by are usually the same group they wish to be accepted by. A single sissy who craves to be laughed at by girls will really want to be accepted by them. A sissy who craves to be laughed at by guys will usually want a guy who will accept them.
It's hard to really get to the root of why someone would crave and be aroused by humiliation. I have a few guesses but most of them are on a very deep and almost subconscious level but they make sense in conjunction with the things I have written above.
For some men, when humiliated by someone they are garnering attention from them, attention that they wanted to have but they had been ignored as a whole by more conventional means. It is exaggerated in fantasy since the attention is usually personal and flirtatious teasing. E.g. this girl that I find attractive who would totally ignore me if I was dressed in men's clothes has now noticed me dressed as a woman and is teasing me, being all flirty and giggly. This is the ideal fantasy case since they aren't ignored or instantly rejected.
For others, I believe that they secretly seek some peace and reaffirmation that their fears/inadequacies are in fact real and but that they would still be accepted with them. E.g. they want to be stripped naked, tied up, and spanked in front of a group of women who will hurl insults at them calling them a pervert, etc. because they deep down feel they are a pervert but at the same time want someone to be okay with that.
The last type I can think of are subs who are a certain way at their core but emotionally haven't accepted that (or refuse to accept that). E.g. a man wants to be forced by a man or woman to dress as a woman since he in fact wants to be a woman. Another example might be a man who wants to be forced by a woman to suck another man's cock because deep down he really wants to suck a man's cock but isn't okay with being gay/bi and this case is okay since it was forced by a woman.
I guess overall, those of us that crave and are aroused by humiliation generally just want our fear and shame to be exploited yet made to feel safe by being accepted by those we wish to be with or having an excuse to do the things that we deep down really want to do.