I'm unclear on what isn't worth the risk? What's the risk?
For ME, the simplest way to put it is that no man could have enough skin in the game for me to trust them implicitly with my children day in and day out in my home and every day life. Personally for me I am not referring to a more casual relationship consisting of bowling dates and ball games on the weekends.
By skin in the game I personally mean having interacted with and been responsible for my kids every day of their lives, interacted with them, loved on them, provided for them, sacrificed for them and put them first before himself. Every single day for years. And loved me, their mother every day for many years before that (10). No man would have had that history. And that's the only kind of man I
personally want involved in my kids' home lives and helping raise them. Other relationships - like coaches, uncles, teachers - those have tangible value yet are different and not nearly as intimate. My kids would not be as vulnerable in those relationships as they would be every day in their own home.
And if a man who was a part of my daily life didn't have enough skin in the game then he doesn't have enough to lose, in my opinion if he makes choices that affect my kids negatively.
To answer your question specifically, by risks I refer to all the emotional ones listed in this thread - those of heartbreak and abandonment. But also just the emotional risk every day of interacting with and possibly even being parented by someone who has not been invested enough in my kids to be trusted to keep their best interests at heart no matter what. I don't know about everyone else, but being a parent is the hardest thing I've ever done. It takes EVERYTHING I've got - and much more - to be the best parent I can be every day. I always joke that it's a good thing they are so cute and that I love them so much - because that's my motivation to make the best choices possible day after day after day. That's my skin in the game. I'm human and my love and devotion to them keeps me in check.
And yes to a lessor extent I do consider any physical risks involved of my kids regularly sleeping under the same roof as a man who is not their father. I am on alert every time we have houseguests no matter who they are. If I have time I will look up links later but have always been under the impression that statistically males are far more likely to molest children than women are. I also would never hire a male babysitter for this reason - just not worth the risk for ME. I get to choose who they spend time with at this time in their lives and am the only one who needs to understand my choices.
As for my extra caution with men I have actually never mentioned it to my kids other than making a point to my oldest DD that I need to meet the BOTH the moms and dads of any of her friends - maybe not for an hour or two of hanging out after school but any time she starts hanging out at someone's house often. I don't worry too much about occasional sleepovers with families whom we know and socialize with. But my radar would ping if she spent a lot of time at one house - especially for sleepovers and it was mostly just the dad there supervising. Not OK for me. The older my kids get the less I will worry. Honestly my views on this are not unusual in our community. Parents make it a point to know each other, even though there is no guarantee there.
About step parents I know there are many, MANY wonderful ones out there - hopefully even the vast majority are. Yes I know there are some terrible bio parents out there, unfortunately, but I am not one of them and neither is my DH. The final risk for me is just upheaval and chaos. Honestly I don't have it in me to add more complications to my life. To add my partner's children and manage my relationships with them and also the relationships between all the kids AND the mother of my partner's kids. I wouldn't do well with all the complexities. I know my vast limitations. I'd wait for another season in my life to possibly seek out a new partner.
Again, this is easy to say when I'm not in the situation. However, given my kids' ages if anything were heaven forbid to happen to my DH now, then it's not like I'd have to wait 20 years before I could seriously date again. It's just a season for me.
I get that many other adults would choose differently for their families and that it would be for the best.