Why do frets wear out?

Because every time you fret a note, you're pressing a string down against a piece of metal and then sliding, bending, and vibrating against it. Do that thousands of times a week for years, and the metal loses. It's not a defect. It's just what friction and steel strings do to softer metal over time.

What wear actually looks like

Divots and flat spots directly under where you fret most often — usually concentrated in the first few frets and any position you play a lot, like a favorite chord shape or a scale pattern you've drilled a thousand times. Over time, those worn spots become low points relative to the rest of the fret, which is exactly the kind of unevenness that causes buzzing at specific spots rather than everywhere on the neck.

Why some guitars wear faster than others

Fret material matters. Softer nickel-silver frets wear faster than harder stainless steel frets, which is why stainless has become popular specifically for its longevity, even though it's harder to work with during a fret job. String gauge, playing aggressiveness, and sheer hours logged all factor in too — a guitar that gets played daily for years will show wear that a weekend hobbyist's guitar won't, regardless of fret material.

What actually fixes it

Once wear is significant enough to affect buzzing or intonation consistency, the two options are a fret level (removing material evenly across all frets to restore a consistent, flat plane) or a full refret (replacing the frets entirely) if the wear is too deep to level without frets becoming too low and thin. Which one you need depends on how deep the wear actually is, not how bad it looks.

If your favorite chord shapes buzz specifically, and other parts of the neck don't, fret wear right in your usual playing zone is a very reasonable place to start looking.