At some of them, there’s a limit to the more. For instance, looking at the schedule for schools my kid is maybe interested in:
Grinnell requires 124 hours / 31 courses to graduate. That’s 16 credits / 4 classes per semester, less one class for unforeseen circumstances. The maximum permissible course load appears to be 18 credits, or 4.5 classes.
Contrast with Smith, which requires 128 hours / 32 courses to graduate, but permits 24 credits (6 classes) per term. And has no distribution requirements, if that’s your thing - my kid is indifferent to them because she has wide-ranging interests and “I’d probably take all those classes anyhow.”
Looking outside her list, at the Ivy end, Brown caps total classes at 40 (average of 5 per term). At Yale, you could probably take 46 (5 per term as a frosh, requiring no permission, then 6 thereafter, requiring a relatively low level of permission), although the theoretical limit is 56 (7 per term).
At the public end of things, my parents still tell me about their days at Michigan State, where they’d take 30 credits each term Fall and Spring, and 20 in the summer, as STEM majors (uphill both ways in the snow, get off my lawn). My current state’s flagship appears to allow up to 19 credits / 6 classes with no special permission.