Carrying the whole group project teaches them one thing: that you’ll do it again.

Covering for other people removes the consequence that would have changed anything. Each time you absorb the shortfall, the arrangement gets confirmed for everyone involved, and what looks like being responsible quietly guarantees the same situation next time. The lesson taught is about you rather than about the work.

Do your own part thoroughly and let the gaps stay visible instead of filling them quietly. Say early, and in writing, what you are and are not covering. Letting a consequence land once is usually cheaper than carrying it indefinitely.