First off, that job fair didn't just spontaneously happen. It was thought up by, organized by, and run by women and enbys in tech, specifically to help women and enbys in tech. Those sponsors didn't just miraculously happen; they were researched, approached, courted, their concerns addressed and their needs accommodated. And yes, that effort too was put in by women and enbys in tech, for other women and enbys in tech.
These are people with limited time and resources, who spent thirty years working on this, who carefully nurtured and shepherded the few resources they could gather, in order to create one single thing to help with their specific needs and challenges. That doesn't mean there aren't other groups with their own needs and challenges - foreigners who need accommodations for their visas and maybe cultural or language help, disabled people who need sign language interpreters or low-vision accommodations, people with issues like ADHD or major anxiety who need supportive environments and some guidance or handholding. There are lots of groups who can benefit from a job fair organized around their specific needs. The fact is, if you aren't part of the group the fair is intended to help, you shouldn't just show up, insert yourself into a place you were never invited, and take resources away from those who those resources were intended for.
And honestly, one of my frustrations is this: if you make a resource for ... people living on Native American reservations, or blind or deaf people, or the mentally ill, or the homeless, or whomever, the resources generated get reserved for that community and no one blinks an eye. But as soon as a resource is designed to help women, there is an immediate and constant demand to expand that resource to other groups. The women and enbys who spent years and decades creating and nuturing this thing have the right to expend their limited time and energy creating resources that matter to them.