But they are simple I-IV-V chords for beginners to use. Adding the Em for a fourth chord is simple for beginners. Plus G is a relatively common key for vocals.
Key of A requires a certain amount of dexterity on the A most beginners aren't ready for as well as F#m.
Using the key of E requires a B chord as well as C#m; again a key most beginners aren't ready for.
Patience grasshopper. The Sabbath, power chords and palm muting will come.....