Here's what the bash man page says:
When bash is invoked as an interactive login shell, or as a non-interactive shell
with the --login option, it first reads and executes commands from the file
/etc/profile, if that file exists. After reading that file, it looks for
~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads
and executes commands from the first one that exists and is readable.
On my slack 10.2 system the default /etc/profile does not have any aliases. All are in my /home/username/.bashrc file. All I can say is make sure that .bashrc is in the right directory and make sure it is readable. It should be very straightforward to add aliases. Is bash your login shell? Check with