I'd be interested to see a breakdown of penalties/prosecutions between main line services and the Metro routes. The latter have a lot of ungated stations and certainly on my local line ticket checks by revenue staff have historically been pretty rare - with one exception, which I will go into. Edmonton Green and Enfield Town may see a blockade, Seven Sisters often gets checks on the passage between the GA platforms and the tube (which always seems to net ticketless passengers with oysters ready to 'tap in' to the tube), but that's about it. Journeys between the less well patronised stations in between have historically been regarded as a free ride for anyone willing to risk it - I've lived in Tottenham 20 years and know a sizeable minority of people are more than willing to. If GA have stepped up on-train checks or set up blocks at lesser stations it wouldn't be difficult to net large numbers, and in that case it probably would be a fair cop. Between Oyster availability and reasonably well maintained TVMs there are few 'excuses' to fall back on.
I do accept more opaque issues such as first class declassification will lead to the sort of PF doleing outs that lead to threads here, but my point is that static blockades at places such as Seven Sisters must regularly pull such large numbers of ticketless travellers that many of the numbers will come from there alone. Six to eight revenue staff plus BTP can be overwhelmed by the suspect cases from a single up train belching out passengers onto the tube there.
