I don't care how upbeat you sound when you say "lunch and learn" it's not going to make anyone want to be there.
@Talia_christine can't relate to this. At my previous job I would do lunch and learns and would only invite our team so as not to bother the others, also figured no one would be interested outside of our team.
And we would have other teams show up and listen in, just word of mouth. It got to the point where I would schedule for our team but drop a link in slack to make sure others feel they are welcome.