I've had the same experience, Yonuh. Though I haven't done it for about 20 years now, In the late 80s and early 90s I taught marketing as adjunct faculty at 2 four year colleges and at a community college.
It was regularly my habit to assign book chapter readings, while bringing in local professionals who worked in the marketing field to speak on topics related to the book chapters. My concept was to enhance the reading with real life experiences.
Then, I would assign a background project, which culminated in a major report due at the end of the semester.
At 4, 8 and 12 weeks, I would give an exam. It would consist of "multiple guess" questions from the assigned reading, as well as essay questions related to the speakers.
The thing that amazed me was that had I graded these exams without a curve, as I would have been graded back in the 70s, everyone would have failed. The students generally scored better on the essay part of the exam, which led me to understand they were not reading the text. However, their language skills were generally abysmal.
I had to grade on a curve, so that someone would end up with an "A."
These were always night classes, the students generally were also working full-time. But I was always surprised at what I perceived as a lack of effort going into the classwork. Most seemed to think that as long as they showed up for class, that was all that was necessary.
These days, when I read that someone is excelling at athletics, while also maintaining a 4.0 GPA, I have to take it with a grain of salt -- I figure the classes they are taking probably aren't too difficult!!
By the way, I tell this as someone who also worked 20-30 hours a week while attending a Big 10 University as a full-time student. At the same time, I was also involved in campus life and dating my future husband. I worked hard for my grades, and my professors held me to much higher expectations than what I saw 15 years later with my students.