Effectively, it was an era before your generation. This is largely speculation, but it's the conclusion I've drawn from my experience in community college (my

Effectively, it was an era before your generation. This is largely speculation, but it's the conclusion I've drawn from my experience in community college (my university experience was more specialized and used effectively no textbooks): Students very often saw themselves as customers to a university, and the consumerist mindset of always being right was unfortunately brought along with this. If they got something wrong, they didn't accept blame for that: they'd push it off onto the TA or onto the professor. One easy vector for that was to blame it on the particular variation of book they had used, so professors started moving towards simply mandating a single golden text and teaching directly out of it. I got the sense that a huge part of it was because the faculty had gotten together and agreed on this solution as the simplest one; it was particularly palpable in cases where the professor was dismissive of and disgusted by the mandated textbook.