I think the difficulty is we know vastly more, and have experimented with vastly more since the 19th century, that the majority of university learning these days, and the inherent challenge within that learning, is "how do we condense 200+ years of investigation, experimentation, and knowledge building into only a handful of years of learning?"

For a lot of sciences, we are very lucky that it is still possible. But the reason why scientists do not allow such an open dialogue with laypeople is because the majority of answers are going to boil down to either "that question doesn't make any sense, and i would have to spend the entire rest of the session teaching you why" or "we already did these experiments a bunch of times in the last hundred years, and found out the result, but the result is tricky because of so and so mitigating factors, and for me to explain these results and how to even interpret them in the first place (e.g. explaining how it was measured, explaining the theory behind why we chose that method to measure it, explaining what the numbers we get mean, etc.) would take the entire rest of the session"

And then of course, there's the frequent crackpots. Pretty much anyone within a science discipline who is even decently well known, especially if they're in physics, gets multiple emails a day from crackpots about how their theories are going to "totally blow a hole in the established knowledge", and at some point you hit a point where you're stuck between "spending 4 hours drafting a response to someone who has not bothered to put in the time to learn physics, and wouldn't listen to you anyway because they think they know it all", and "getting actual work done in your field". The scientists I know do take time out of their day to answer actual questions from inquisitive folk, but the difficulty is that thanks to the addition of ChatGPT, those questions are getting more and more cramped out by the crackpots armed with a hallucinating dictionary.