This is the main reason.
When I attend these events, I enjoy it and find it interesting. But as soon as time passes on (say a week or two), I feel like I wasted more time on these events than necessary because it messed up with my schedules and deadlines. The extra time comes as result of follow-ups after the event, the wait-time for decisions, and so on. If there is no follow-up, then it will not be beneficial at all and it loses all the purpose of having to attend it.
So it's hard trying to find the right balance between these things and work. Therefore, I asked the question so that even if I attend few of these events, I can create reliable connections out of it instead of having to repeat the same process repeatedly? Hope this clarifies a little bit more.