I've heard a lot of buzz about this product called bb cream. what makes it so popular?

BB Creams: Cosmetic item sold mainly in east & southeast asia, but larger beauty brands (garnier, dr. Jart, dior. Sephora, clinique, & maybelline) are introducing it to western markets. Due to its "multi-tasking" all-in-one properties — moisturizer, primer, foundation, and sunblock — the cream is a hit in asia; some perceive it as anti-inflammatory. No apparent scientific studies to support claims.

Its marketing.: Big in asia, it's being marketed in the U.S. Now too. Besides being a moisturizer, it also includes a sunblock which is probably the best thing you can use for your skin!