Why, mainly, do people work in Primark or in a cafe, or with members of the public? What is the main purpose of their relationship with their customers in that situation? If they are employed by an organisation, and found to be, e.g., attempting to coerce, abuse, or defraud people in that environment (either fellow employees or customers), they are/were under contract and they will face penalties and can be removed if they are found out. They do indeed have training for their role: not safeguarding, but training that sets out the expectations of behaviour. Both they, and the place they work for, have responsibilities.
Now what about volunteers, in a place where they will very probably meet vulnerable people? The ethos of a church promises that you will find community, that people will support you and aim to work with the principles of helping people who are distressed, sick, troubled, feeling guilty, struggling sometimes, and there are not all that many churchgoing people who would deny that at times, this could be you, or your kids, or your Gran.
And a lot of the practical stuff offered, including even the cups of tea, will aim to centre this in how it is offered.
There isn't the protection of a contract or 2 sides of a till, or 50 minutes of a therapy hour. There's a toddler group or 2, maybe a youth group - but that's not a nursery or a school, or whatever you want to assume of this place. So yes, the vulnerable will be there.
I'm really glad to read that there are some people who say 'I did make a safeguarding referral but that was because of what had come out of the training'. I don't love training, I'm sceptical about some of it and I can disagree with it, but I do see it as part of a volunteer role of this kind.