Buy a ticket and get on was the standard everywhere for trams and trolleys because you didn’t have enough enforcers and you didn’t have controlled access.

Spot checking kept people honest but it only really works when most people are honest.

And it is common to cheat, as it is cheaper to pay the fine than to buy a pass annually. Naturally, this is done more by the foreigners I know than the natives. But the foreigners are not Japanese...