Why is Girls' Generation so wildly popular nowadays?

[TrucV.]

Being a huge fan of them myself, expect a long explanation!

Each member is different, and with SM being such a high top company, it's most likely their are known. Because SM produced pretty much every artist on the Hallyu Wave, there was DBSK, now TVXQ, BoA, Kangta, Shinee, SUJU, F(X), SNSD and of course, EXO's debut is a huge thing right now. SNSD had trained over various periods of time and plus SM has put them into musicals, dramas, and they endorsed lots of advertisements, it could because of Yoona, she has made an early debut as an actress thus becoming very popular, and being pretty and a good dancer, she got the spot as the face of the group, plus many male idols have SNSD members as their ideal types, it gives them attention but SNSD's fanbase is pretty harsh but very caring, causing attention for them. Recently, SM had SNSD debut in America with the English version of the Boys, and they appeared on 2 popular night time interviews, they also had SMTOWN concerts in international countries (France, California, Japan) and they made a huge success in Japan with their tour. Not only that, each member is currently busy with something making them known, and SNSD is known for their beautiful figures and beauty, synchronization, addicting songs and dance moves and their charming personalities on variety shows. (Many shows ask SNSD to appear on them)
Yoona- filming Love Rain drama
Yuri- filming Fashion King drama
Sooyoung- preparing to film a medical drama I believe
Jessica- finished filming her drama Wild Romance
Hyoyeon- Invincible Youth 2, and Dancing with the Stars 2
Sunny- Catch Me If you Can musical, host (I think) and Invincible Youth 2
Seohyun, Taeyeon and Tiffany- Music Core hosts and currently acting as TTS (SNSD's subunit, their video reached 10,000,000 views within about a week, showing their popularity)

I think it's because of their company, SM has trained artist to work their very best even to fatigue, and they are trained in acting, singing, dancing, etc. but SM not only focuses on talent but also visuals.