Putting it mildly, scientists are somewhat passionate about their work. And like any person with a passion for a particular topic, once you get them going you can't get them to shut up. I guarantee that if you walk into any random faculty office (please knock first), and start asking curious, honest questions, you'll be there for hours.
So why aren't scientists out engaging with the public more often?
There are of course a few challenges to public outreach from the perspective of a scientist: difficulty in translating the jargon, fear of saying something inaccurate, discomfort in presenting to large crowds, and so on. But scientists are some of the smartest people in the world - surely they can overcome challenges like that?
They can...if they're incentivized. But the modern academic system actively discourages public engagement. The number one focus for a researcher is getting grants, followed closely by writing papers. Teaching and serving on committees are also on the list...somewhere. I suppose they also like to spend time with their families.
What little time that does get devoted to outreach is usually done selflessly (with no net benefit to their tenure or advancement prospects) or to satisfy some thin requirement in a grant. Most scientists want to do outreach, but are limited in their opportunities. Unfortunately there are no easy answers to this dilemma, except to create as many frameworks as possible to make it easy for scientists and the public to connect. In other words, if scientists can’t come to the people, the people have to come to the scientists.