Ironically, it all came down to Metallica's disgust toward opportunistic music industry suits. After the tragic death of bassist Cliff Burton in 1986, the band decided to take it slow for a while. However, due to the success of their previous album, the group was receiving a lot of pressure from their handlers not to kill the momentum. In order to appease their capitalist overlords and break in their new bass player, they figured they could remove two bat heads with one bite by recording a five-track "practice" EP.
The end result had a garage band feel ... because it was literally rehearsed in a garage, then quickly recorded in a studio in six days. Also, it was all cover songs.
Metallica's management did not object, knowing that at the time they could release an album of James Hetfield farting into the microphone and still make tons of money out of their rabid fanbase. Hell, they could probably squeeze 10 bucks a pop out of this cheaply-made crap! Metallica's reaction? Titling the collection The $5.98 EP: Garage Days Re-Revisited, explicitly referencing its small budget and small workload when compared to the albums they gave a crap about.
"Honestly, we put more effort into our handwriting than the songs."