The problem is that the amount of work required in collecting statements, photos and writing it all up and then getting the brigade to consider a prosecution is immense. Then you have to ensure compliance with PACE - not a bad thing in itself, but it means that any 't' not crossed or 'i' not adequately dotted may result in the case being thrown out and costs incurred on a cash strapped authority.
Add to that the sometimes horrendous task of identifying the Responsible Person and the whole exercise is one that many IOs avoid and many RPs manipulate.
The introduction of FPNs should be for minor/first offences. With a 28 day appeal mechanism to allow for over zealous IOs (if there are any!), the punter should be well protected. The process of preparing a full hearing/prosecution should be retained and reserved for more serious offenders.
Let's be honest, most businesses only really respond to the threat of financial penalties as reminding them of their responsibilities by 'educating and informing' or sending a 'Notice of deficiencies' is seen by many as a soft option. A "we've got away with it" mentality.
In my area, there are FPNs for parking, litter, fare evasion and even not having a licence for an 'A' board advertisement outside your shop!!!!. But if you have a potentially serious FS issue, you get a lovely (free) enforcement notice with details how to comply, 28 days to appeal and an (often infinately) extendable time limit
As CivvyFSO said, maybe we are being too nice!