Great band, but the answer to your question:
1. their singing was weak
2. their songwriting was weak
You can usually get by with lousy songs if the singer is fantastic (example: All Right Now by Free, did Paul write the words when he was still in kindergarden?) or lousy singing with fantastic songs (Dylan, Lou Reed, Neil Young).
Even though I've owned a number of their LPs since the 70s, I find that every one of them has 2-3 killer tracks and a lot of filler. "Hogwash" is probably the best of them in that respect, the bass tone on that one is killer too...sounds like he's using barbed wire for strings
At their best, they merged a quirky blues feel with mellotron, synths and pulverizing volume, sort of like Black Sabbath playing Pink Floyd covers. Good soundtrack for rolling fatties...
