Many others already pointed out the usefulness of meeting others and learning from them (or even socializing, if you're that kind of person).
I'd like to stress out a point mentioned by Todd : being able to ask question to specialists. When the meetups are great (from my own point of view), it's because:
Since the best conferences are all other the world and expensive, I'm just not able to attend. Hence, like you, I learn a lot from the internet and have long playlist of talks (either the good ones I liked, or the ones yet to be seen).
But so many times, either there's no time for Q&A, or is was a conf and there was no Q&A, or there was, but nobody asked the question I had in mind.
And then, to answer your question, I could probably find the answer on the internet... but I might find diverging answers, and not know which one to trust or is optimal, or I could only find partial answers and would have to try... all to say that it hardly compare with being able to ask it yourself to an expert who is there to share his/her knowledge.