Because it was all about timing. Remember his first album cracked the Top 10 on Billboard, but Death Row was pretty much done by then, and it didn't get much push. After that he went the independent route and made some noise, but really no one was giving the West Coast any play, and when they finally did, you had to be Dre, Snoop or Xzibit otherwise you were ignored.
Also, he flooded the market with subpar releases. So much so, that I pretty much stopped paying attention. I was buying that shyt, too. R.A.W., Dillinger & Young Gotti, Tha Dogg Pound Gangsta LP, This Is the Life I Lead were good, but DPGC: U Know What I'm Throwin' Up, Gangsta Crunk, Dillinger & Young Gotti and So So Gangsta had too much filler.