As much as Scott Weiland was the key to the Stone Temple Pilots uprising, he was also their downfall.
If he had not been an addict, had he stayed sober or even just sober enough to keep touring strong, STP could've been as big as Pearl Jam now, even bigger maybe. But the band didn't tour nearly enough. The biggest fact contributing to this: Scott Weiland. As a result of this, the Pilots fell off the radar as a mainstream band as far as their "new" music went. We all saw how Shangri bombed compared to any of their other albums prior, this was not because Shangri was a particularly bad album. Sure it wasn't as commercial, but it had its fair share of songs that could've been huge. I do agree the management and marketing for STP wasn't great either, but say you're a major label giant, you've got this band that already made you enough money with its early stuff, that now has an unreliable junkie lead singer. Would you continue to push this band as hard as you could? When the band failed to tour properly for Purple, that is when things slowly started going downhill...
Just my two cents
~A drunk 8 pm rant from NSC
Edit: For the record, I don't hate Weiland, I love him just as much as you guys, but it is what it is