Why most folks can learn to play!
We will need some definitions for this post: "Chord" - Any group of three (or more) notes. Popular groups get names and symbols. "Common Chord" - The most popular chords. There really aren't many of these.
The reason that many tunes only use common chords is that the writers and publishers of these tunes want to sell them. It's a financial reason based on what people like. They like common things. They buy common things.
The two most common (and thus popular) types of chords are majors and minors. Huge numbers of popular tunes only use them. Additionally, they only use common "keys" as well, but that's another discussion. The reasons are the same, money and sales!
You should focus on mastering such common chords.
