I've long imagined that the situation was not so much can't, as that USA/NASA/people have become more risk averse. It was OK that the people strapped to the top of a Saturn V might die when y'all were fighting to "beat the commies", but to put people on the moon, again, ...?

Interestingly, China germinated plants on the moon this year, but that news seems to have been buried in the UK. So getting a payload to the moon, guidance systems and such, isn't the problem.