People just don't understand
Hip-Hop albums and R'n'B albums are very different. Rappers a lot of times have established and loyal fan bases who will buy their music regardless, and a lot of rap listeners have enough respect to go out and cop an album that they feel should be supported. I mean, how often do you hear people say "This album is worth buying" or "I'm gonna spend my money on this"? A lot.
In R'n'B and pop, all of that music is built around singles and hit songs. Their radio smashes sell, their image sells, their concerts sell, and their popularity sells. Outside of hip-hop, albums are on "Who the hell buys albums anymore?" status. That is exactly why 2Chainz outsold Trey Songz, I mean who the fukk is an actual loyal supporter of Trey Songz?
Only in hip hop and select genre's/artists do you hear "I'm gonna cop this album". Yeah, you'll find that in country and rock music, but definitely not in pop or R'n'B.
Regardless of what people think, these teenage white girls aren't buying all the albums. Most of them likely pirated it from some bootleg pirate MP3 site like "newhotpopmusic.com" or some shyt.
And at the end of the day, Trey Songz is still more respected than 2Chainz and became famous off of 1 or 2 radio hits, while 2Chainz had to build from ground up, change his name, and grind for years just to even come close.