My following comment is not about clothes, but not long ago I washed some curtains that were hanging in a window for some fifteen years. The amount of lint that came out in the dryer was incredible. I'm talking inch-thick wad on the filter screen, growing another inch with continued drying, after being removed.

It was probably due to years of UV breakdown of the fibers from daylight.

Or accumulation of (invisible) hair and clothing fibers by the coarse curtain fabric over the years.