Thought I'd add my two pennies to this conversation.
I've just had a CEL PCN appeal upheld, thanks entirely to advice from this forum.
Years ago, when less risk averse, younger and crucially - had no kids, mortgage nor a serious job and therefore had more time - I would fight every ticket I received. With the help of Pepipoo, and some self learning, I managed to win every single PCN battle. Brilliantly, I also told family members and they to, time willing, won several appeals.
I remember winning those appeals at The Angel, then going for a celebratory pint each time at (I think?) The York, just up the road from the appeals office. It was often easy. Rarely did the issuing party turn up, and sometimes they didn't even send the paperwork. They even on one occasion sent a representation for a different offence, car and date....
I was always 99% sure I'd win going into that office.
Thing is, those days I lived in London, and could afford the time to attend. Several years later, and faced the option of £60 - £100 versus the effort of going to London, even to win, the fine feels like the sensible choice.
It was only really that I found myself hacked off with the injustice of it all that I Google'd Pepipoo after all these years and followed the paper trail here.
I guess my point is this - busy people (which is most people) would rather through gritted teeth suck up a penalty. They don't know what recourse they have, and even when they do, it feels too much of an effort.
I've confused council issued notices with private notices above purposely, because therein lies a problem. The whole system needs full reform, with a single penalty fare set by central Government, with a single appeal place for both private and council issued PCNs. It's wholly ridiculous to expect the average motorist to be aware of their rights dependent upon where and when they received a PCN.
Ah, but how can Government impose a flat fine for PCNs I hear the cowboys cry? Easy, amend the act to state that EVERY issuing body must be a regulated body and therefore adhere to centrally set fines and standards, with centrally set appeals processes. No sign up, no authority. And penalties for organisations that issue PCNs who haven't signed up. If a vehicle is parked illegally and can't be removed, it's a police matter (which will swiftly get the police on board with encouraging those that issue PCNs to sign up).
Returning to the issue of whether or not a recipient of a PCN chooses to challenge - under a regulated agreement, the appellant is offered recourse at the collective expense of those who (must) join the regulated scheme. This has to follow a process of issuance, and right to appeal. If the appellant wins, it is an the expense of the issuing company (including travel costs, time off work etc). You have to make it clear, and cost neutral, for the person who receive the ticket. If it worked properly, you could even have a triage centre (which is where the more experienced members here could monetise it) to inform the recipient of the likely chances of success - which is essentially what you good folk here do for free.
Ultimately, IMO, people just don't have the time to fight. But if provided with a free recourse system that was made abundantly clear from the offset, with the option of triage to weed out the no hopes, and if that was regulated to make sure it was clear on every single PCN, that's the only way more would be encouraged.