Because it’s a massive franchise. When you go into a Starbucks they want it to taste the same no matter where you get one. People are creatures of habit and it’s easier to get someone to get the same thing than it is to try out local shops wherever they go because it might be bad or too different from what they normally prefer. It’s one of the reasons fast food chains are / were very popular in the US. It’s not about the quality, it’s about the consistency
I mean you say that, but I went to a similar school in the US and the professor had his own book. It was cheaper than the old textbook and to top it off he “warned us” not to go to a certain site and download the PDF version. Some professors care and it’s more about the administration than their own opinions.