Skill unlearning impossible with some Skills

I can't lvl down the following Skills, is there a reason for?

- Thrust (actual 5)
- Riposte (actual 12)
- Blade Speed (actual 28)
- Bludgeon (actual 5)
- Ranged Combat (actual 5)

 

@Paladin Michael, Skills have minimum requirements for the preceding skill(s). This also means that each skill has a minimum skill level below which it will not decay. This minimum skill level is based on the requirements of child skills in that skill tree. A skill cannot drop below the point where you would no longer qualify for any child skill. For example, the Bladed Combat skill will not decay below level 40, as child skills like Riposte require Bladed Combat be at least that level.

Until a skill reaches this minimum skill level, it may only be set to Training or Not Training.

 

Thank you Alley Oop,
I know about this, but why can I lvl down other Skills back to zero/one point?
For what reason shouldn't it possible to regain the xp points for an unused skill tree.
Especally when no higher Skill is used in the same row?
For example: the grey one Blade speed.