Hi Massimo, I am glad you asked this question as I think it does cause some confusion.
I twist all residues of old stems to remove as little root as possible and disturb the soil as little as possible, but to remove enough of the old plant that it will not grow again. Chervil for example would resprout if cut at soil level, and residues that are resprouting can get in the way, and offer little to eat., compared to new plantings.
I am puzzled that you needed a fork to remove the roots, perhaps you are trying to remove too many roots. The main bulk of them can certainly stay in the soil and will rot down to feed everything following, it is only the main stalk or stump of old plants that need twisting out. If soil is dry and hard, almost no roots will come out and that is fine, certainly better than digging the soil to remove them.
So TWIST and just be sure to have removed the base of stems, at soil level and just below, which could otherwise initiate new growth of the old plant. This applies to pretty well every above-ground vegetable.