I hired many college graduates and always reviewed their transcripts. So, from my memory of over a hundred engineering transcripts; GPA’s were pretty constant over the 4 years for most, some rose varying amounts, a very few went down.
The full grade drop that I have heard about is from high school to college.
Certainly not a scientific study and may not be representative of all colleges.
My GPA was one that rose over the 4 years. I improved my study skills, got into study groups and was more interested in the upper level classes were the reason for the change. My son’s GPA also rose some while my daughters was pretty constant. A family of engineers.