That's a problem that has more to do with the program itself, as some of the teachers basically refused to fail students unless they didn't show up at all.

Oh certainly.

Nevertheless, your little "enabling contribution" is still a significant (and important) part of that system (and thus a significant part of the underlying problem).

In fact, your behavior is exactly what is expected -- the system KNOWS that you will "cover" for your teammates (and thus be part of the collusion/delusion that the other students are learning) -- which is actually one of the REAL and primary reasons for the groups/teams in the first place.

I didn't take their tests for them also.

There are other ways that the system accommodates this; and colludes to hide/mitigate the effect of failure: everything from the way the majority of tests are constructed (the very commonplace 4-option "multiple-choice" with the "Who wants to be a Millionaire?" style array of answers); along with the final grade being "on a curve" and even without that, the acceptance of partial mastery (i.e. 7 or 8 out of 10) as if it were "good enough" to demonstrate comprehension of the material & concepts. Note that the reality is that anything less than 100% -- on a test that is VALIDLY constructed to ascertain mastery of the concepts, rather than inane trivia -- in fact demonstrates the opposite.

While my hard work certainly gave them a small boost

Actually it taught them -- and you -- specific "social" lessons.

They learned (or rather had the lesson reinforced) that it is unnecessary to actually learn or comprehend anything, much less perform the actual "work" themselves; instead they learned (or again, had reinforced since they obviously learned the point years prior and throughout their schooling) that burdens can nearly always be shifted off onto some willing patsy, and most importantly without losing any of the credit (much less incurring any formal shame or discredit) themselves.

And YOU learned -- to the "socialization" system an equally important thing -- the lesson that you are supposed to compensate for the inadequacy of others, and that the "system" is setup to penalize you if you don't; moreover you are habituated into an internal sense of superiority, while actually becoming the functional inferior to those lesser than yourself. IOW you are primed into the "sanction of the victim" mentality (i.e. getting you ready to be a "happy serf" later on {though doubtless there will also be some "frustration," the systems have ways of keeping that from generally becoming too harmful}).