Does one of these apply to the area of Keswick?
The Road Traffic (Permitted Parking Area and Special Parking Area) (County of Cumbria) (Borough of Copeland) Order 2003
The Road Traffic (Permitted Parking Area and Special Parking Area) (County of Cumbria) (Borough of Allerdale) Order 2003
The Road Traffic (Permitted Parking Area and Special Parking Area) (County of Cumbria) (District of South Lakeland) Order 2002
The Road Traffic (Permitted Parking Area and Special Parking Area) (County of Cumbria) (District of Eden) Order 2002
The Road Traffic (Permitted Parking Area and Special Parking Area) (County of Cumbria) (Borough of Barrow-in-Furness) Order 2001
The Road Traffic (Designation of Permitted Parking Area and Special Parking Area) (County of Cumbria) (City of Carlisle) Order 2001
If so then the reason is simple. Decriminalised parking enforcement.
The council makes up the restrictions. The council charges for permits. The council makes money from payment of penalty charge notices. You don't get to go to a real court to contest.
It is a government/council run scam.
However, in a council owned off-road car park if you are done for "not parked whole within a marked bay" you MUST check to see if the car park actually has any bays. You might be mistaken for thinking that the lines on the ground are the bays, no... The official bays are marked in a document. It has been known for the council to forget to mark any bays on this document, and therefore you can't be done for not parking within a marked bay because the whole car park is the bay.
Under DPE the council have to do everything perfectly. They often don't manage this. The wording on the penalty charge notice has to be perfect. The lines and signs have to be perfect (on-road anyway). The traffic restriction orders have to be in place correctly.
And if you can't manage to find something they did wrong, don't forget
The Coinage Act 1971 when paying your debt. Especially Section 2 - Legal Tender.