Every company design their own USP and target market.
giffgaff want you to use the £10+ goodybags, everything else is pitched to cover their costs.
All prices are based on a balance of costings to cover their costs, which for PAYGO members includes free gg to gg calls
For instance if everyone maxed out on free minutes then the cost of goodybags would rocket.
What you actually pay for a goodybag is based on what the average member uses.
The same applies with landline prices unless you have a call plan BT charge 13p/min plus a 22p setup charge - ouch!
The bottom line is, look around the market and choose the supplier with the price/service offer that suits you.
giffgaff is not for everyone, free gg to gg calls, and the lack of a long contract is a major plus for many.
The likelihood of gg offering a 1p/min etc is virtually nil.