Take the NQY operation as an example, a route I know from old, one might easily and regularly transport 120+ passengers a day each way to/from LON but it wouldn't work putting a 120+ seater jet on the route once a day, or indeed a B747 on the route twice a week, the only way those figures may be achieved is by operating 3 or 4 services daily on appropriately sized equipment.
This is an important point with regard to
shorthaul flights, and the reason, for example, why LHR's capacity problems cannot be resolved simply by using larger aircraft as suggested by some.
Minoan were doomed doing OXF-DUB and OXF-EDI,
especially without advertising, because they were up against neighbouring airports doing those routes with way more frequency.
JER may be another matter entirely.