In many areas, the junior and senior level classes at selective LACs are equivalent to grad courses - check out catalogs. That’s why these students have no trouble getting into Grad Schools and figure high on the list of where PHDs got their start.
The exception is math, if the student is taking Diff Equations in HS rather than AP calculus for instance, and some foreign languages. However foreign language courses can be more advanced, it really depends on the college. (For a practical experiment, compare the courses offered this semester in French at Brandeis, Northeastern, and Denison. Add Bryn Mawr, Middlebury, BU and Lehigh or University or Miami. Then choose a less commonly taught language of your choice.)
Generally speaking, national universities will offer more languages at the beginning level, from Polish to Swahili to Korean. However there may not be a major in each. If you’re unusually advanced in a sequential subject you encounter specific challenges in finding an appropriate college.
What subjects are you interested in @waittheday?
For other subjects, since you can only take 4 or 5 courses per semester, you wouldn’t lack choices. Even a small LAC will offer close to 800- 1,000 classes and 5 or 6 advanced classes in your subject each semester, ie., more than you can take. However you do have more choice among these courses at the upper level at a national university, especially if you already know you want to specialize, say, in military history or biological anthropology. Just as with students who are unusually advanced in math and foreign language, this doesn’t matter to most students.
Where are you attending school right now and why are you asking? Are you interested in applying even though LACs aren’t well known in your country, are you just wondering what in the world these colleges are, …?