no one knows the real reason, but in my opinion they got new competition in young but very successful Chinese phone manufactures who sell fairly good products for less money. Second Samsung have to stop to sell us half-baked products for high price, for instance galaxy Alpha has ridiculously weak battery, S5's design is awful, and they did not make inovative flagship phone since S2 and S3... we will see what S6 is going to bring us
