Some cats cannot clean themselves therefore they mat (knot).
Cats naturally express oils in their coat to prevent them getting wet.  In winter a cat builds up a winter coat for insulation.
cats remove their excess oils and undercoat by licking,  this causes hairballs.  Not removing enough oils and undercoat (under grooming) leads to matting and dandruff.
Your cat may not be removing its own undercoat and oils, due to; excessive oils, excessive undercoat, old age, arthritis, being overweight, or being lazy. I can bath and blow-dry most cats to remove excessive oils and make your cat feel like a kitten again. Please do not put scissors to your cat as they cut easily.