What keeps you coming back to cons? Even /cgl/, as small as it is, shows there's a billion possible combinations to explain: "Why?" Some answers, but definitely not all, would be
>Cosplaying
solo, group, admiring, meetups, photography
>What the event itself offers
Guests, shops / artist alley, rave, game room
>The social element
Parties (unofficial), hookups, meet new folks, mutual friends flying in from different areas
>Hanging out
People watch, the weird experiences only cons can provide, that one time in the year "the gang gets back together"
And of course any reasons I forgot to include are always encouraged. The floor is yours, gulls.