Now, I'm hardly going to advocate spending decades in a dimly lit basement learning the most archaic aspects of music theory that nobody outside of six wizened elders in a tower presiding over whatever music school you feel to be sufficiently prestigious enough to warrant building an arbitrary tower, nor am I going to expect you to have a tuning preference between 440 and 442, but I will suggest you learn the basics, and I have a good reason why: It's super easy, and it makes playing easy.

If you want to make up a song, and you've already got a good rhythm and a chord you like, knowing some simple theory will tell you which chords are going to sound good together to finish the song. If you already know a song, but playing it has gotten a little stale, some simple theory will tell you where you can play which cords or variations on the chord shapes to make it interesting again. If you're going to play with anyone else, knowing theory will let you know what they're playing and let you decide how you want to play with them and instead of just fumbling around trying to decide what sounds good with what's being played, you'll already know what's going to work before they change to the next part of the song and what to do if they do something unexpected. It's the difference of being a few steps behind everyone in the dark, and being a step ahead in the daylight. Theory can help you see what you're doing and where you're going. And I'm only talking about strumming chords here. The best part is, it doesn't change the way you play.

Also, if you look at what either of those bands were/are actually doing, you'll notice that simple isn't really an accurate word to describe them.