People about Cosplay...
It depends on what you mean by popular. It’s more or less exclusive to conventions, which have the benefit of only happening once each year per con. Attendees like myself have time to craft and sew awesome things. I know why I like it-it pushes my creative boundaries and has become my full time hobby and side-job. It’s very fun to be someone else, but it’s also fun to show off your work. I made my husband a great Groot costume for DragonCon last year and it was one of the best weekends ever. We had a blast as ‘Rockette’ and Groot. There’s something about participating in a huge fandom that is just pure fun.
I don’t think it’s really all that popular with the general public, when people don’t know who you are it can be disappointing. They don’t really know what to make of you when you come into a restaurant painted blue with a handful of storm troopers after an event or convention. Kids seem to go nuts over it though, I’m also a member of Rebel Legion and dress as Princess Leia for events. Adults are amused but kids go crazy for Darth Vader. Popularity really only seems to stretch as far as known characters.
I’m going to address this question from a different viewpoint. Why is cosplay popular amongst those that do it?
There is the factor of honoring the source material/fandom that you love. There is the creative outlet. Then there is the sharing of the work with other fans and making new connections with like-minded people. Getting complimented for your work can create a sense of accomplishment, as can having a photographer ask to take your picture. A three day event like a local comic-con or Anime/SF/Fantasy Convention can be more rewarding than a two week vacation in the tropics, to some people.
This all has a spillover effect, those that aren’t doing it, see the results and fun that those that are having and want to do it themselves next time. This keeps the world of Cosplayers growing at a currently staggering amount. I’m staff on a 2,200 person Anime Convention and we are constantly amazed at the ~60% cosplay attendance.
I enjoy comics too, mainly Judge Dredd, actually nothing else to think about it. I’ve got T-shirts, computer games, loads of comics / books, an Oyster card wallet, badge and cufflinks of JD. You could say I’m a fan. At comic conventions I take interest in seeing the various folks in costume. It’s not my thing, but I get their enthusiasm.
One of the team on my current client in Holland is a huge Star Trek fan. He has all the films and all the episodes. At the moment he’s collecting a part work of all the space vehicles. He goes to events but hates seeing anyone who dresses up and is out of character. “No one from Star Fleet smokes, carries a beer or spends their time on an iPhone”. He doesn’t do cosplay but appreciates those who take the time to add something to the atmosphere of an event by doing it well.
Watching my shy 8 year old and his 10 year brother with the Star Wars guys at a convention made my day. These people enjoy spreading joy. To me, that act of generosity is a big appeal.