Dolly Parton wears wigs because they are practical, theatrical, and completely part of her brand. For her, a wig is not a disguise. It is a stage light you can put on your head.
The practical reason
Big blonde hair takes time. Wigs let Parton move between performances, interviews, travel, and public appearances without rebuilding the same style from scratch every day.
The image reason
Dolly's hair is part of the character she created for public life: glamorous, funny, exaggerated, and instantly recognizable. A wig keeps that image consistent.
Does she hide it?
No. Part of the charm is that she talks about beauty work openly. The wig is not a secret; it is part of the craft.
Bottom line
Dolly Parton wears wigs because they give her speed, control, and a signature look. The hair is show business, but the honesty about it is very Dolly.