It's all about disclosure. By way of example DL's rock bottom E fares, described above, appear in a separate column and with a warning. If you book one, it's not because the restrictions are buried.
These represent good value for people who don't care for anything other than transportation from A to B. There are people who are on tight budgets and are quite happy to be assigned a middle seat at check-in and manage to pack just a simple carry-on.
Needless to say, the greatest risk is that there are no changes permitted of any kind. Thus, if you do need to take a later flight, you must buy an entirely new ticket.