I understand entirely the point the OP is making, and, to an extent, agree. The problem with any rule enforcement is to balance effectiveness with convenience and cost. TOCs could guarantee every passenger held a ticket if (as an extreme) every passenger was accompanied by an official with an electronic key card at every point of their journey from ticket office to final destination. So all other options involve a compromise. The key to the compromise is effectiveness, increasing the chance that a traveller without a ticket will be caught. Barriers, including manned gates, can be effective, but are not infallible - the equivalent of fixed speed cameras on the roads. IMHO, more effective is the random ticket inspection, if carried out frequently enough, always creating the fear in the naughty traveller that they will be caught but they cannot predict where - the travelling speed camera. OK, this means that some journeys will not have checks. It's a compromise.