If the learning experience is simplified to listening to a lecture, either live or recorded, and all grading is done algorithmically, then yes, there is no scaling limitation. This would be considered a very poor learning experience though. Even in the School of Engineering at Harvard, even for the CS classes, very few use autograding. Students expect individual feedback on their work. They expect the ability to personally interact with teaching staff. They expect group work, labs, office hours, reading groups, and some level of supervision over these activities.

I work at Harvard, and I can tell you there is a real push to create a quality experience in remote learning, and a lot of resources are being directed towards this. It is not just the same classes via Zoom. Of course these enhanced learning environments could be replicated on campus as well, there's nothing particularly special about the remote learning environment.

But as you suggest, it is the residential experience that most folks are paying for. Harvard considers the residential experience as one of their primary value propositions. That is why Harvard and other schools are working very hard to get students back to campus. It's a difficult balancing act between this and maintaining the health of the campus. A major outbreak amongst undergrads would be a serious blow to everybody involved, so health is always going to come first.

Also worth noting that 20% of Harvard students pay 0 tuition, and more than 50% get needs-based scholarships. https://college.harvard.edu/financial-aid. So if you're smart enough, and/or fit into the financial aid brackets, why not go to Harvard? What's the risk there?