Training Day I have a family acquaintance (let's call them "Charlie") who likes to do things for other people. The things Charlie doees aren't what other people would actually want (and are actually sometimes against their express wishes) and usually impose extra work on other people to take part. Charlie then gets annoyed if everyone else isn't
grateful for all the effort Charlie put in.
Even with the day described from your own point of view, you're taking away a day of operations to supply people with a set of information that
you have decided that
they need to have. It doesn't sound like you're being at all discriminating, trying to "cover off" everything, so for any given participant there's a good chance that a lot of the information will be irrelevant to their role, or a repeat of things they've heard before. You're "bringing in" people to do the training, so the quality, consistency, and cohesion of the presentations could be all over the place.
Now, I'm not saying that your day will actually be like this, but that's a typical experience people have of training days. That's what some of them will be primed to expect. The question you should ask is not "Why are they negative?" but "What am I doing to subvert their expectations?" They are entirely right to be skeptical, it's up to you to prove that they are wrong, so that they come up to you afterwards and say "Thanks, that's not at all what I expected. Good job."
A starting point might be to ask them about their experience of previous events, so you can make sure you don't repeat the things that have created their current attitude.
(I'm often one of the people "brought in" to speak at company safety days. The experience is highly variable. Some are planned months in advance by professional event planners who vet every presentation and ensure they blend into each other with a consistent yet interesting message. Others have mix of internal "death by powerpoint" and external "here's my generic talk I give at 200 workplaces a year" with bad AV and poor time co-ordination.)