Activity based costing

hello

I have a doubt relating to variable o/h costs.

First of all, this is what I have understood about variable production and variable O/H costs:
1. Variable production costs
a. Short-term variable production costs – cost driver based on the volume of activity
b. Long term variable production costs – ABC based cost drivers
2. variable O/H costs
a. Short-term variable O/H costs – ABC-based cost drivers
b. Long term variable O/H costs – cost driver based on the volume of activity

Sir, Now here are my questions to you:
Q1 why don’t we use cost drivers based on the volume of activity for Long term variable production costs?
Q2 why are long-term variable O/H costs are not allocated using ABC-based cost drivers?

Thankyou!