According to NME, Dave Grohl opened up about his time in Nirvana and why he didn’t sing or write any of the songs. He said quote, “
"I didn't like my voice, I didn't think I was a songwriter, and I was in a band with one of the greatest songwriters of our generation. I didn't really want to rock the boat." He said in a CBS interview when he recorded the first Foo Fighters in '95 he didn't even think it was a record. Read more here