I forget precisely how the transfer papers were printed, so apologies if I get this slightly wrong, but not only did the driver have to give you the transfer paper, they had to punch it a couple of times to define its parameters in order to ensure it was a "legitimate transfer." An example of an illegitimate transfer they were trying to prevent would be taking a northbound bus, popping into a store, then using the transfer to complete a round trip on the same bus going south.
Transfers were a buck, over a base fare of $1.75-$2.50, depending on when (IIRC), so they were hardly an incredible savings anyway.
My point is there was an elaborate system requiring bus driver time and thought which was there to prevent regular riders from saving a tiny bit of money, adding delay and inconvenience to the entire system.
With the introduction of various smart card/contactless schemes in transit systems over the past couple of decades, such things have diminished, but I want to highlight the thinking behind it which was, basically: we will sacrifice simplicity and convenience and bus travel time, reducing the appeal of the system and likely *overall revenue long term*, to ensure that none of our scum passengers saves 75 cents individually.
This isn't a post about my local transit system, really, though such things are/were incredibly common in transit systems especially. That kind of approach to things is common everywhere.