What would make a nice man from a normal, uncomplicated, middle class family choose to keep getting involved with women with so much baggage?

It sounds like you get that this now the pond in which he realistically fishes, and so does he. And tbh the way you describe your upbringing, solid middle class and stable rather than say obvious trappings of money, it might not have been as desirable as you might think to women looking in.

Other than that, some people just never settle, and as time passes they become more likely to find each other.

I think one could be seen as a mistake. But more than that indicates something about him.

I've had one chaotic ex. I wouldn't touch another one similar, ever.

I'd say this. As a person who considers herself 'nice and normal', I'd not touch him with a bargepole. He sounds chaotic and unstable. Someone with a string of recent failed relationships at his age isn't a good choice for anyone hoping for a LTR.

Why did he need the most looking after of any family member - there’s your answer I think

What’s not flattering is people moving in and out of adult relationships forgetting the DCs needs, whatever class they are.

So...he is quite derogatory about women who have lives like this (with multiple factors making them potentially vulnerable) yet actively chooses to form relationships with them?

🚩🚩🚩🚩🚩

He likes the drama? He’s controlling and co-revive? He’s immature and wants a mummy figure?

I don’t believe anyone has said it’s only ever men. But the OP was asking about her brother

Yes, I'm a man. My account name is supposed to be a clue but I accept that in this thread I didn't make it explicit. The general Mumsnet view is that a man posting and explicitly saying "Man here..." is doing it wrong. So I generally don't.

No, I've never left a woman holding my baby. Quite the opposite in fact. I was a single parent to my children from when they were entering primary school.

What I'm trying to say is this: yes, women don't have a monopoly on drama but neither do men. What the OP describes is a man with a child and an ex - or "baggage", as the OP so delightfully describes them - meeting women with children/exes/"baggage".

To highlight the OP's brother as apparently thinking with his dick sets a viewpoint of him being some kind of predator to these helpless victims of his dastardly wiles. Yet he's in much the same position as they are - he's got a history, he's got responsibilities for his prior life, and he's . Why assume that these women are helpless, incapable of making rational choices and/or are making decisions for different reasons than he is? Surely it's not only men who want to have a relationship with someone because they enjoy having sex with them, is it? It's not only men who happen to fall in love with people who might not tick all the boxes of "sensible choice with a good salary and low LTV", is it?

If both parties in the relationship have a history and children from prior relationships, what makes the man the villain and the woman the victim? Do they not both have agency, choice and the possibility of thinking with their gonads rather than their heads?

Many 24 year old middle class boys would seriously consider someone older and more experienced. Ask any woman on dating apps in her 30s and 40s.

So that's the first relationship.

A youngish single dad isn't going to be first pick for childfree women unless he's objectively very attractive or very rich

(a mortgaged home with some equity and a "professional" job title and child maintenance isn't a lifestyle with lots of disposable income).

Since then I expect it's been a domino effect, dating other parents, as that's his dating/social scene.

After a certain age people who are single and childfree often aren't really genuinely interested in relationships, or will require a high level of incentives.

It's a big change and compromise to start any relationship, let alone be a step mum.

Add the fact that many men often value physical attraction way over job status.

His dating pool now isn't actually that large if he likes a relationship and doesn't like being single.

A lot of people really thrive in busy family environments without being overly concerned about how it looks, or any long term implications.

If he seems content I'd just let him be and emotionally detach from the situation.

Maybe he likes looking after other people. Did one of your parents expect him to look after them, either emotionally and/or practically?

Life can be funny, you could end up like one of the women you describe.

It’s low self esteem. He’s surrounding himself with these people so he’s the superior one. He can’t be bothered to compete with the rest if you.

And your brother is helpless in their conniving, chaotic, vixenish grasps, clearly.

Can you just say what you want to say? Because I can’t believe you don’t know the answer to the question you’ve asked - unless you’re a man who’s left a woman holding his baby.

My family also looks "stable middle class". No drugs, no police involvement, no spectacular problems. It took me a lifetime to realise families can be abusive in ways that are not obvious.
The most sensitive children are more affected. From your posts I'd assume your family was dysfunctional in subtle ways and your brother is more sensitive.
(BTW, I seemed to have a successful life. Academic achievements, married, 2 kids, husband with a good job. No one knew what was really going on)

If they're immature, lacking emotional intelligence, thinking only with their vaginas etc then where do those additional concerns and considerations come in?

If you didn’t have nice middle class parents and a nice middle class husband, could you have afforded to establish and maintain a nice middle class home-owning lifestyle?

Either way you’re a snob, but if you sit in your ivory tower thanks to deposits from parents and a second income from your husband, you’re also a hypocrite.