I'm not sure you can, because they'll automatically go on the defensive as a matter of self-protection if you frame it as a criticism - and that's what they will hear, with this approach, no matter what you intend.
(Why do I say this? Because they're already turning you down. They've already invested in saying no - they're not saying "I would like to, but..." and explaining. That means they're distancing themselves. At this point, anything that seems like criticism to them will only result in more distance. Yes, it sucks. It's what people do, though.)
If you can frame it as an open ended question, and (most important!) if you can set aside your feelings in the moment and try just to focus on what they say, and take it in, and not react even if you think they are totally wrong and what they say is painful to hear, then you may find out what you need to know.
It can't be about *telling* them anything - it can't be about your emotional need. It absolutely has to be about a need for information, only. And you really have to be able to set emotional responses aside as much as possible, to focus on that information, or it won't work.
This is hard to do for anybody. For the best chance of success, pick the least drama-addicted and least socially competitive among the ones who are saying no, and ask that person. In a neutral setting. And try not to react to their reply except to ask neutral, clarifying questions, and to tell them thank you. Then, whatever you do, don't talk to anyone else about what they told you - if you decide to ask others, treat those conversations as totally separate.
This is a lot of emotional work, but it's the best way to defuse tensions going in, and it's the best way to assure, as far as you can, that you get useful information out of the discussion(s).
Believe me on this. People are strange - the more you need from them, the less they're willing to give, much of the time. But you can, if you're neutral and objective, possibly find out why you've been hurt. It may not make sense, it may be totally unreasonable, but what is important is first to find out why. After that, you can decide how to follow up.
Good luck. If it helps at all, I've been there, and when I asked, I found a small group of my colleagues who resented the hell out of me for having actually done and learned the things I'd done and learned that were on my resume. This came out in the way they responded to careful questions. There was nothing there to fix. Those particular people just sucked, individually and as a group. I was able to write them off, though, with a clear conscience after that.
_________________
"I believe you find life such a problem because you think there are the good people and the bad people," said the man. "You're wrong, of course. There are, always and only, the bad people, but some of them are on opposite sides."
-- Terry Pratchett, Guards! Guards!