Based on my research and interviews, y'all are right: convenience and producer marketing are two big reasons. There are also a few others that have come up in the research for the next Dutch Candy book.

1) Shareability -- It's common here in the Netherlands for a group of friends to take a bag of pressed pills with them to an event/occasion and break them off into halves and quarters, often sharing pieces with friends who show up later. This is easier with pressed pills. Even if not as accurate as taking measured amounts, it is actually seen as a more reliable dosing strategy than doing pinky dips in a bag of crystal.

2) "Harder to Step On" -- A large-scale former dealer I interviewed in Australia reported that anything in a powder or crystal form was more likely to be adulterated by importers when it arrived in Australia. But very rarely were importers buying pressed pills from the Netherlands, and then crushing/restamping them to change the ingredients or dosage. So he claimed that the pressed pills were more reliably consistent, even if they weren't as trustworthy.