The most common reason for this happening is that the shell profile for the new users doesn't have any settings to adjust the shell prompt; plus it also depends on the shell that is configured for the user.
when I do:
useradd -m freddy
Then su - freddy, I get the prompt
$
and the ps listing:
$ ps
PID TTY TIME CMD
7258 pts/28 00:00:00 su
7266 pts/28 00:00:00 sh
7300 pts/28 00:00:00 ps
i.e. not using bash.
if we add the user with the bash shell,
userdel -r freddy
useradd -m -s /bin/bash freddy
su - freddy
we get the prompt:
freddy@host:~$
If you want to modify the login shell of the user accounts so that they will have a prompt, then you can do:
usermod -s /bin/bash <account name>
for each of the accounts.
Again, all the useradd, userdel and usermod commands are performed as root!