It's all fine and good that lounge staff CAN (and do) print BP's for any number of reasons, and gate agents can and do - again for a number of reasons. A change to self service not being able to print them will add workload at the various staffed points - be it in the lobby, lounge or gate.
And gate agents are usually busy enough as it is trying to get a flight out without joe bloggs wanting a paper BP for whatever reason because they couldn't do it online.
And yes, it's an ever diminishing number that probably want them (or need them due to tech or other issues) but I am sure the bean counters have a cost factored in per pax for this kind of interaction. ie each "can you print me a BP?" interaction is probably a minute or so of work per staff member. Maybe 30 seconds if one hands over a QFF card with barcode to scan. Those add up. Specially at a busy station with multiple flights and reduced levels of staffing.
I wonder if QF have thought this through and prepared for it.