I also imagined something like that. Maybe with a provision for trains that are not in the app and have to be added manually.
But we don't know what the average milage per travel day is, for example, and what the final income per km travelled thus would be, so it's actually quite hard to say if that's low or not, compared with the average income they have from general ticket sales.
You're right, we don't. We have our own experiences (which as enthusiasts will probably mean high mileages) and we have anecdotal evidence from our non-enthusiast acquaintances and their offspring etc.[possibly a bit more representative]. I think it is probably true to say that, in Northern Europe, it is likely that most people buying a pass will be travelling quite some distance (I have never heard of anyone in the UK buying a global pass and only visiting Belgium and Netherlands for instance), heading for sunnier climes or maybe an adventure in Eastern Europe or Scandinavia.
Presumably because of the flat fare of the global pass, people in the centre of Europe are probably less likely to buy one (unless doing multiple journeys), as ordinary tickets may well be cheaper for the more popular destinations, as it will be for people going on a relatively short journey. This will likely mean that the majority of global passes will be bought for trips where the reimbursement will be at a considerable discount to the point to point fares available for the journey. Which the long distance railway operators clearly do not like at all.