Why people attend reunions?

Organzing a reunion can be a daunting task. But if the committee understands "why people attend reunions", it should  be much easier.

After attending more than 25 reunions in past 6-8 months, I have understood the motivations of alumni attending reunions.

So what does a good reunion look like?
It is meant to be a fun party where people meet their old classmates, have a nostalgic time, and a section of the attendees would want to network for professional purposes.