Why would anyone do it apart from vacation or hanging out with old buddies?
Conference participation after getting tenure
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To learn new things and keep up to date.
Wouldn't the same time be better invested in reading some interesting new papers?
You need to know which papers are interesting to read, conference participation is one way of learning what you should be reading. EJMR is another. Staying on contact with people in your area is another, and conferences help with that. Plus they are usually fun. You can attend too many though you need to show up ate least once every 2-3 years for people to not forget about you.