Never noticed this, visited Japan a few times myself. Often I had mine checked at the gate and on the train. Are you sure you’re not just exaggerating?
I recently visited and totally noticed a lot of minders, caretakers and other seemingly unnecessary jobs, mostly carried out by retirement-age employees or retired volunteers[0]. It was weird but seemed to make sense from a societal perspective, quite heartwarming.
I visited Japan recently and although I think the tickets were only actually checked by one person, there did seem to be an awful lot of superfluous staff associated with any sort of transport.
Could it be because you're a foreigner? I almost certainly got picked out on every ride on the Munich S-Bahn by a fare agent for a ticket-check because I was obviously not German.
Which I totally get - a tourist is way more likely to make a mistake than a local.
It has been my impression, having spent a significant amount of time in Germany, that German ticket checkers aren't primarily trying to detect people who have made a mistake, but those who intentionally ride without paying.
This information may be a bit dated, but I visited Berlin circa 2008 and my friend (American expat) who had been living there for 10+ years insisted that we not pay at the subway, because no one checked. Following his guidance, I never paid for the subway, and was never fined. This was just within the city of Berlin, though.
[0] https://haywirez.com/tokyo-hong-kong-2018/