sudo as another user with their environment

$ whoami
admin
$ sudo -S -u otheruser whoami
otheruser
$ sudo -S -u otheruser /bin/bash -l -c "echo $HOME"
/home/admin

Why isn't $HOME being set to /home/otheruser even though bash is invoked as a login shell?

Specifically, /home/otheruser/.bashrc isn't being sourced.