In addition, at many institutions such tests are given infrequently and can be worth a significant component of a student's overall grade, increasing both student stress levels and the tendency for such assessments to measure short term knowledge students have obtained by cramming, not more meaningful longer-term knowledge gains.
I see you're giving quizzes every three weeks, which is better than twice a semester, but still not what I would consider an ideal cadence. In my course weekly computer-based quizzes comprise 70% of a student's grade, but that's supported by a significant institutional investment in high-frequency computer-based testing: https://cbtf.illinois.edu/.