I think crond was never enabled in DreamOS images. Why? no idea. But I know that some team images and GP3 have special plugins for crond and enable it.

But for today: Why not use systemd timer units? They are superior to crond and should work out of the box
https://wiki.archlinux.org/index.php/Systemd/Timers

systemctl enable busybox-cron.service

does not work to start crond on bootup?