I'm not a guy but grew up in a family that didn't do emotions. My parents are really logical, clearheaded people, so they felt like emotions were an annoyance and unproductive. Even after years of therapy, I still struggle to cry in therapy even when I need to. I feel stupid and weak when I cry, like I'm being a bratty child.

So A) it can be really scary and vulnerable to cry in front of someone
B) even more vulnerable in front of someone you don't know (such as a therapist)
C) we totally get it.

And also, like others have said,
D) they're used to it. It's what they do. My therapist uses the metaphor of a car mechanic. When you take your car to the mechanic, he doesn't really care about judgments. It's not his job. His job is to fix the car. He said, "Oh, look, you've got a leak in your radiator, let me fix that." He's not frowning on you because of something happening in your car. So my therapist says I don't have to worry about what I'm bringing there or if I'm crying or not. His job is to help, not to judge.

In the end, please know that when you find a good therapist, it's safe to cry there. And then you're not hurting alone. They are there with you in the pain.